Well, reading anything at the library is way better than buying a book and reading it at home for two reasons.
1. You don't have to buy the book, therefore saving money for more important things.
2. You read them WAY faster in the library.
Like someone (Pam I believe) said before in this thread, a toddler can read each book in probably less than an hour sim time. I have also noticed that when my sim is reading a skill book and I make them read it until they level up, they finish way faster than the game says they will, usually be several hours. For example, I drag the action bar thingy to the right until is says "read until level up" or something, and it says that my sim will be done at 9:00 PM when in actuality, they level up at maybe 6:00 PM or even 5:00 PM. It makes such a difference, it's crazy. I love using the library for skills like cooking or logic that for me seem to take forever to level up in the higher levels by cooking or playing chess. If they have a want to reach a certain level in that skill, or they just want to level up, I send them to the library for an easy skill level.