Changing barrels

I see a lot about changing barrels here on the forum and lots of advice on how, I want to know "why" or maybe more correctly, is it a good idea to do often?

I have a 12BR in 308 and I want to maybe shoot 260 or 22-250 as well. Can I simply keep a couple barrels around and swap them out like lenses on a camera? Same bolt face so I don't need to worry about that. I need a vise and a nut wrench and cheater bar/small steel hammer for a "rap" to tighten the nut.

I can figure out the point of impact issues just fine I think but is it a good idea or do you simply get new barrels on when your old one is shot out?

Me, I tend to get one I like and leave it on for awhile. However, others tend to change barrels more often then they do their underwear. Nothing wrong with either method. I would think that after a few thousand barrel swaps the threads may get loose :D.