It would help a little to have it before you apply. Generally dental schools like to see that you have taken as many upper division science courses prior to applying. Although they do not penalize you if you have not taken any specific ones.
I think it helped me on the DAT a little bit. I do agree that like any upper division course it increased my understanding of the topics I learned in intro bio. But you can do well on the Dat without having biochem as well.
So bottom line is yes it would be nice to have it (especially is you think you can get an A/A-, which is very hard to do in biochem), but don't think of biochem as a course that will make it or break it for you. Unless you fail it, in which case it will significantly decrease your chances of getting in.
Just whatever you do DO NOT take it your fall semester when you are apply to DS.