The common advise is to not split the party. In fact, it often goes NEVER SPLIT THE PARTY. And you know what? Normally it is pretty good advice. It could even be considered a rule. The fun thing about rules though is that if you understand them, know why they're there, and why they work, you can break them.
Today I want to talk about splitting up the party.
The Danger of Splitting Up The Party
The danger in splitting up the party is that games are often designed for the party to be together, and so if they split up things get rough for them. A fight meant for the whole group is probably going to roll a single member of the group. And this is double damning because while those few people are in combat the game slows down...which means the others are just watching, powerless to help.
It can be very rough. And this is why the advice/rule is often said to players. Don't split the party because it just leads to getting everyone killed. Divide and Conquer is a tactic. Why give the GM the easy card of dividing yourself? Right?
The Challenge of Splitting Up The Party
On the GM side of things there is a challenge to splitting up the party. Mostly this is balancing the spot light. The fewer people who can be in a scene together, the longer every individual has to wait for things to get back around to them. The longer someone has to wait to get a chance to act, the more likely they are to get bored. Very little sucks more than sitting at the table all session watching everyone else play. Sometimes it happens despite best intentions, but it is something to try to avoid.
The more you split the group, the faster you have to switch from sub-group to sub-group to keep everything going. The more scenes you have to balance at one time. The more pressure and confusion you're going to get, especially if two groups jump into a combat in one go. And this is why we also tell GMs to not split the party. It makes things exponentially harder, not linearly.
The Benefit To Splitting Up The Party
There are benefits to splitting up the party. In game, the PCs can accomplish multiple goals at the same time. They have increased risk, but also increased reward, and that is a good thing. They can cover more ground. Do more things. Check more areas. Meet more people. Employ their separate skills to greater effect and with more efficiency. You know, all the reasons people split up in movies, books, and shows.
From the GM side, it also provides an interesting challenge, and can really shine a spot light on the group in new ways. How do those characters fight when the healer and sniper isn't with them? How do the healer and sniper fight when they don't have the tank with them? What tactics are employed? What opportunities are opened up? How can you challenge the character now that you couldn't before when the group was there to cover up for all their weaknesses? How can you emphasize their strengths now that they don't have to worry about covering for someone else?
As an example, the Rogue/Ranger in one of my D&D games has gotten to go off alone scouting or infiltrating several times recently, and in doing so has been able to showcase just how good he is at stealth, deception, and disguise. Skills he doesn't get to often show off, or use to their full benefit, because the rest of the party can be very loud.
It Also Ups The Tension
If you're ready for a split party, one thing you can do is give the PCs multiple goals that are mutually exclusive. Two places in a lot of danger, both of it happening now. They can go to one or the other but not both....unless they split the party. This is a sort of third option, but it is interesting.
In splitting the party they may doom both places. They may also save both places. A task they were sure they could handle together may be more challenging, and less sure to be done with only half. Who do they send where? What are there priorities? What is in the balance?
It is not something I recommend doing all the time, but here and there it can be really fun to do. Just don't punish them for splitting the group. If they walk in unprepared they do that. But don't just smite them with giant encounters because they're trying to be heroes.
Don't Smite Them?
The reason PCs are taught to 'fear' splitting the party is getting into encounters too big for them. This happens often because the PCs are forced into encounters that are too big for them. No matter what they do, the GM springs the encounter on them.
Try not to do this.
If the PCs are being loud and not paying attention, sure, it can happen, but if they're being alert and cautious? Play into that tension. Let them know what could be coming. See how they play it out. See if they can get around it. Give them a chance to use those skills they may not get to lean on all that much.
If the fight happens, hopefully they'll know how in over their head they are. Just be clear and be careful. Having PCs willing to split up to do things is a big boon to a game in a lot of ways. Don't punish them for it for the sake of it.