I've been gaming for twenty years, GMing for a bit more than 75% of that, and to this day I still struggle with when I should call for a dice roll and when I should just hand waive it. As the years have gone on I have strayed more and more to "less die rolls is better." It may not be the right answer, but it is the one I think works the best for my games. I'm still working on how few, but lately I've been reading some good advice on it and I wanted to share it with you today.
Two Thoughts On When To Roll
The advice I've seen on when to call for dice rolls seems to fall into one of two categories. The first is "you roll when there is a significant chance of failure." The second is "you roll when failure could make the situation more interesting." Of the two I prefer the second. Why? Because while chances of failure being significant is not a bad metric, it does have some problems. Chief among them is a lack of consequence for failure in many situations leaving you with the situation of having to also deal with re-tests and things of that nature.
What Makes A Situation More Interesting
With my hat, primarily, in the camp of you call for rolls when a failure makes things more interesting then it stands to reason that for this advice to make sense we need to define what makes things interesting. The key to that definition is in the problem to rolling for significant chance of failure above. A failed die roll should make things more interesting by bringing about consequence.
Consider a situation that we would normally call for a die roll. Let's say Sharon is playing a thief that is trying to crack a safe. Sharon rolls and she fails the roll. What happens? If the answer is "she doesn't get into the safe" and nothing else then it is a bad thing to call a die roll for. I'll repeat that: if the only consequence to a die roll is no forward motion, then no die roll should be called.
If the party needs what is in the safe, and they have managed things that Sharon is basically alone and not threatened with the safe, just let her in. If it is bad for the party to get into the safe, or the safe's difficulty makes it extremely unlikely for Sharon to be able to crack it in one try (say she needs a 16+ on a D20) then just tell her she can't crack it right now. We'll get to what to do in the situation where the player still wants to try later. For now though, just keep this in mind: a failed roll needs more consequence than just back to where the player was before the attempt.
How Do We Make It Interesting Then?
This one is simple. you make things interesting by adding in other consequences. Sharon wants to crack that safe, right? So instead of rolling to see if Sharon can crack the safe, roll to see if Sharon can crack the safe without setting off an alarm. Alternatively, roll to see if Sharon can crack the safe before a guard walks in on her trying to open the safe.
With both of those a failed roll has consequences that make things more interesting. Sharon fails the roll, an alarm goes off. Now she has a choice: does she stay and try to get in anyhow, or does she bolt? With the other option Sharon is also brought to a decision moment, a guard has walked into the room and seen her. Does she flee? Does she fight him? Does she try to con the guard?
This can be harder with some skills, but even then you can always do something. A character tries to play the flute for the King's court. What are they rolling for? If they succeed they curry favor with the king, put him in a pleasant mood, and likely gain some fame. If they fail? The opposite can and should happen. Embarrassment, loss of fame, perhaps even being asked to leave or unincluded in future events. If the player doesn't want to risk being ejected or losing glory they can just say they are playing the flute (they have the skill afterall) and the performance is simply what it is: neither super effective on the mood of the people, nor terribly grating.
Other Rolls and Extreme Situations
We're back with Sharon and the safe. Only, her party has gone to extreme measures. She has the whole building to herself for the night. The security company has been told to ignore any alarms because the IT company is doing tests on the lines. There is absolutely nothing that could happen that would prevent Sharon from having multiple shots at the safe. What do you do then?
Personally, I'd just give it to the players. I mean, that is a lot of effort to get that time with the safe, and with the amount of access they'd have I don't see the safe surviving it. However, it could be that the safe is another player's stuff or that there is a time constraint that while not a factor for the safe is a factor for the PCs beyond the safe (i.e. they need to get what is inside the safe to someone by noon the next day, but still have 12 hours to mess with the safe itself.) What do you do then?
Well, then it is time to change the scope of the roll. Ask the player how long they're willing to try to crack the safe normally before they go to more extreme measures. The roll then becomes "can you crack the safe in that amount of time?" and degrees of success then make it faster but failure means that they can't. How is not cracking the safe in that time interesting? Because it eats time the PCs need for other things. Everything else becomes more tense because of that failure, and that keeps it interesting.
No time constraint? Then maybe you just roll to see how long it takes. A bad roll makes it take a long time, and now you have other problems. The security company is concerned why the tests are taking all night and want to send some people down. An employee needs to get an early start and shows up early. Something happens, just make it interesting.
Which Way To Hand Waive
The last detail for this is to know which way to hand waive. The trick I use for this is I compare the PC's skill level to the task at hand and decide based off of that. Can a PC with Safe Cracking 2 be expected to crack an Expert level safe? If so, then yes Sharon can do it. If not, then no Sharon can't do it. The safe is just too advanced for her level of skill. Does that mean the PCs can't get into the safe? Not at all. It just means that Sharon isn't going to be cracking the safe without some change in circumstances (she skills up, gets help, gets much better tools/information, or gets that mythical level of access I talked about above.)
This is something I'm still working on, but to state it simply: you should only call for a die roll when a failure would make things more interesting in some way. Never ask for a die roll if failure just leaves the PCs exactly where they were before the roll. Just hand wave it, even if it means saying that they can't do something right now.