Is it alright to split yarn into its separate ply's to make it go farther?

Usually when you split yarn into its separate plys, it breaks easier. Even as you are knitting, if you split the yarn with your needle and then continue across the row, those stitches become weaker and will be more likely to split apart.

I have been knitting/crocheting for 15 years, and would NOT ever recommend this. There is not really anything you can do to make yarn "go farther", you just buy more yarn, making sure you buy ALL you need for the project at one time. It is possible and has happened to me, that you don't actually start a project for awhile, or you finish a project LONG after purchasing the yarn, and it has been discontinued. Thus leaving you with either an unfinished project, or having to rethink the one you haven't started yet.