My horse is on pasture board, he's out all the time. Most horses (one they are used to each other after a couple of days) don't scuffle much so kicks and bites and scrapes aren't happening all the time. But I have special "horse spray paint" that I use to cover any cuts/scrapes for showing. :)
Some times, with a horse that is really disobedient under saddle, or has an attitude problem (and has been turned out and it doesnt seem to help) people will leave the horse in all the time. The horse gets worked at least once, sometimes twice a day until it starts to bond with the person and learns that work is something to look forward to. It is especially effective with a horse that is abnormally bonded to it's pasturemate.
My friend used to have a pony that was obsessed with my horse. She spun and took off and snapped the lunge line once, ran right over and stopped outside of Bailey's pasture to kiss him over the fence. It worked very well with her when she was "forbidden" to see him, and was forced to bond with her owner instead.
Other than the extreme case, I think horses (especially TBs) need their down time to be a horse and run off the extra energy.