Bolt-on necks although extremely popular with cheap guitars, are also found on some expensive guitars and some famous artist use bolt-on necks for the percussiveness you can get out of a guitar with that type of neck. Set neck is as you said glued on with the addition of the wood joint. The only way you may foul up a neck is if you tightened your strings beyond the recommended limits. Bolt on necks are replaceable though. Set necks, ehhh I've heard people say you bust a set neck and your screwed, I'm not really sure. Now if you bust the neck on a neck-through guitar, you are definately screwed. So a bolt-on neck would be the safest type to experiment with different tunnings on. There used to be a whole bunch of post on here about the differences. I'm not sure if they are still around though.