No boot "supports" so when you are talking about polo wraps supporting, it's minimal. Maybe quilts and standing wraps, but I know very few people who ride in those (and I never would). The polos do protect some from interference and striking, but not as much as a boot would.
That said, I LOVE polos, both for looks and because in the wetter season my sensitive skinned mare gets washed and blow-dryed every day on her heels and fetlocks, I like to then wrap her with polos when I ride to keep the indoor arena sand off her fetlocks.
My gelding? He just looks **** classy in 4 white polos.
ETA: I do not let other people polo wrap my horses. It can be done incorrectly and do damage by uneven wrapping. I learned how to do it from a dressage groom who did it so much she had perfect wraps every time, and practiced until mine looked and felt just like hers.
Some horses like the pressure of the wraps on the legs...one of my mares does much better when wrapped. And I agree...they just look nice IMO :) Not a lot of actual protection except against small nicks.