I have not enough space. The folder is too big.

Besides: When I restore the whole system, is the new system completely the same as the original one? Could it be that I get problems? Could it be that the restored system runs slower or something like that? In other words: Is a restored OS X as good as an original OS X?

->I just have a little problem in my system, but I cannot find the cause. That's why I want to restore the whole system. Is this the wrong way to solve my problem?