I don't know it it's going to make it any easier for you to get into a specific law school, but it certainly won't hurt.
You'll get tons of brochures, and business cards. You can ask questions, and most of them offer you a sign in sheet, which allows you to show your interest, and to receive e-mail from them.
I went to the LA one last year and plan to go again in November, now that I am actually applying. I really want a chance to show my face, let them know I'm interested and what my situation is.
Up to you, but I say anything offered is a chance to show how much you want to be in law school. Just make sure you don't ask them anying questions such as, "Why should I go to your school?" or "What makes your school different?" After all, we should be selling ourselves not asking them why we should want to go there!