I've got nothing to say. If a level is too hard you deffinetly need a walktrough. If you have once been very close to victory that means that you already know what to do. I mean if the level is starting to make you rage then the way how to relax is watching a walkthrough or asking a friend or an AG user. So they are useful and necesarry.
I never use walkthroughs. I like to figure out how to do stuff and I don't feel any victory if I have to rely on someone else to tell me how to win, because I like finding a solution myself. But hey, that's just me.