Thin, thick, soft or hard rails. Please explain.

Before posting this I tried to research old posts to see if my questions can be answered but I had little luck. I figured I'd start a new post on the subject just incase any other newbies need educated as well. Explain what each term means and what is gained or lost by each board design. The only take home message I have learned is that hard rails (i.e. the sides of the board are squared off...more at 90 degree angles) allow for better bottom turns, carving, manuverability. I guess if you're a newbie/ wobbler you'd want soft rails because you just want to maintain balance on the board and if it keeps a straight line you have a better chance of maintaining balance? Please fill in the gaps, I'd like to learn more on the subject especially if I'm off target on what little I think I know about it.