The three spells listed in the topic are three of the more "bread and butter" high damage spells of the mage world in most D&D games. However, that isn't all they are. They also represent something to keep in mind when you are GMing because they are the three formations that a group of PCs can be in when they are adventuring, and when they are fighting.
What do I mean when I say formations? Well, I mean that the formation of the PCs is best - and most efficiently - destroyed with one of those spells. Not that you have to use those spells, but they do have things to keep in mind, especially when designing a particularly nasty part of a dungeon or a particularly mean wizard-like NPC.
Lightning Bolt is the most basic and easiest to understand formation. It is a straight line and you most often see PCs in it when they are walking down hallways. This is the standard formation most people picture when asked for a "marching order" for the group. Often the fighter/beef tank is near the front, back up fighter near the back, and the squishies or glass cannons are in the middle where they are best protected. As indicated by the title, this formation is most vulnerable to lightning bolt as the spell passes through EVERYTHING in its distance and can thus zap the whole party (reflex saves failed obviously.) However, it also means other things as well. For example, an obstruction in front of one party member can cause problems with turning about. It is easy to grab the squishies as they're trapped in the middle, you just need access to them from the third dimension. There are lots of fun things you can do here.
In many ways Fireball is the opposite of Lightning bolt. By definition a fire ball covers a wide area, and why? because the group is scattered. This is the formation you get most commonly after a few rounds of combat, especially if no one is giving tactical advice to the group. The rogues have often ventured off for back stabs, the fighters have moved up to engage, and the casters have scattered to prevent something like lightning bolt from getting two of them at once. This is also the formation with the least coherence for the group as there are open pathways to any member at any time. You don't see fireball formation out of many seasoned groups, especially if they played in the era of the "Evil GMs" where things like this would be taken as a great reason for a high level sniper to suddenly draw a bead on the mage.
In this one, you want to pressure your PCs with the fighting. These represent very dynamic situations and so having people trying to rush by to get at the less defended squishies can be a fun way to heighten the drama - and stop those wizards from nuking your big bads in the process.
Cone of Cold
By now you've probably figured it out, but cone of cold is when the group is spread out but not so much that they can't support each other. A spell like Cone of Cold can get them all, but lightning bolt can't. This is the most common formation I've seen experienced groups get into in combats, where the fighters and rogues stay close enough to defend the casters and everyone can benefit from each others talents. In many ways the Cone formation has some of the best strengths of Fireball and Lightning Bolt for the PCs. However, it also has some of the weaknesses. One of the chief ones being that it isn't any good unless you're in open quarters such as a big room or outside. The other being that there are still gaps in the formation to get through, and still the possibility of trapping people in the center of their friends.
Why Am I Talking About This?
I'm generally not in the GM vs PC camp, so why am I talking about this? Well, for one, it has been in my head all day. For two though, even if I, as the GM, am not going to be trying to kill all my PCs, that doesn't mean the enemy NPCs aren't going to be. Thinking about the formations can also be a good way to be prepared to spice up combats when the moment is right, and having them categorized down into 3 easy to remember attack types also works well.
I'm sure there are dozens of other tricks to use to do the same thing. I'd love to hear yours. Sound off in the comments!