Yeah it's not mandatory, but I liked taking them both anyway.
Just make sure that whatever you do, study for both sections Equally. I took the psat and got a really high math score, but a low critical reading score, so needless to say that I crammed a lot for the CR section and didn't worry about the math section so much. I didn't do terribly on either section, but my math score was considerably lower than what the psat had predicted it should have been. So be sure to study everything.
Hope that helps.