Correct me if I'm wrong. I have tried the method Bret, ASG and MJ all mentioned before but found it rather inconvenient. Because, for example, if you want to apply the same delay (same plugin, same delay time, same feedback amount, etc.) to both the lead vocal and the lead guitar (but not to background vocals and rhythm guitars), you'll have to create two effect buses and insert exactly the same delay plug with the same settings to each of the buses, and then route one of them to the vocal bus and the other to the guitar bus, because if you route them to the master bus, the balance between the dry sound and the wet sound won't be the same when you adjust the volume faders of the lead vocal/guitar tracks. Does this make sense?
So, if you want to apply effect to the whole set of instruments (e.g. compressor, eq, saturation, etc. to the whole drum kit), you should definitely create a bus for that purpose. But if you just think it would be convenient to adjust the volumes of multiple instruments with a single fader, I suggest a better way, which is simply grouping all volume faders of tracks of the same instruments (group all volume faders of all guitar tracks, for example). This grouping feature isn't available in all daws, so why not take the advantage? You can avoid creating unnecessary buses this way.