Originally Posted by: RazboJust my 2 cents: If you stick on some part until it's perfected you might bore yourself right out of trying to learn any more.

That's true. Everybody has different levels of frustration tolerance. You'll have to figure out your own. When working through a book, some people like to perfect everything before moving on. For others, that approach can be very tedious, and it may feel better to move on to the next exercise even if it's not down perfectly. In the second case, you may work your way through the whole book a few times over, instead of progressing through the whole thing once at a slower pace.

As was pointed out, there is the danger of memorizing the piece you're working on, and then not actually sight-reading it but playing it from memory (with the notation as a reminder). Of course, if you're just learning how to sight-read (and getting used to notation simultaneously), this may not be a big deal in the beginning. But eventually, you'll want to test yourself by putting brand new pieces of music in front of you and having a go at it.