Cons: Fairly pointless for science students? As a 2nd year maths, I didn't go there until the other day and that was only because I have to write a stupid essay.
Meh, that's hardly a con; more the inherit nature of a library and science courses If you're sufficiently keen and enthusiastic to read around the subject in maths/physics, the library does have tonnes of material to help you though
The online resources of the library are pretty good - it allows you to access Athens / MathSciNet / various other papers and journals from the comfort of your own home.