Buff Possiblities
It's true what they're saying - buffs don't do anything, and they are just placeholders. But if you are making custom abilities, it can be very useful to keep tight control of your buffs, because you can assign triggers to check for them.
For instance, this is a neat little combo I've used in the past:
Let's say you're making an RPG and you want the character to be able to sleep to regain health and mana (there are MANY ways to simulate this... but read on). One way is to make a copy of the standard sleep spell, and modify it so that it can only be cast on allies. Give the spell to a building or something where the hero can rest - let's say a tent. Then create a custom buff that the ability can put on the target (In my map, I called it "Resting"). (Note that sleep actually adds 3 buffs - the "stun" and "pause" buffs don't need to be changed, I just replaced the "sleep" with "resting") Now you can create a trigger:
-Every 1 second
-set RestGrp = all units matching condition: (boolean) matching unit has buff "resting"
-pick all units in RestGrp,
-set life of picked = life of picked + 10
-set mana of picked = mana of picked + 10
-destroy RestGrp
Obviously, that is just a shorthand ver of the trigger - you gotta be careful of memory leaks, but there are many in-depth tutorials on that on this fine, fine website.
But the point is, now you have a sleep spell that also heals the target! The normal sleep spell still works normally because it assigns a different buff.
By paying attention to your buffs, you can use triggers to add additional effects to established spells. The sky's really the limit...