I'm not sure you can make a blanket statement. One of the schools that accepted me offered one to all students and required it of some, mostly students who had been out of school for some time. From what I have heard, they make things easier for the first few months and even out a weak foundation in the sciences. But it's probably highly variable from one school to the next. If you know what school you're attending, I'd join Facebook groups for not only your class, but the ones ahead of you, and ask around to determine if they're worthwhile.