What are the main benefits of working out forearms?

Now the same question but how about for someone involved in mixed martial arts?

I have been researching this lately myself and all I have come up with is low iron levels. I'm having a similar problem with bruising. Small bruises have began popping up on biceps when I work out, but I don't use equipment that requires pressure against body so I know it's not from pushing or rubbi...

I usually do 175 situps a night and I almost never feel them. I did 500 the other night and didn't feel them, not even the day after. Is that good or bad?

Oh, and I don't do them in a row. I do them in sets of 30 and then the final set it usually to round off to total.