I'm not a fan of polos for exercise at all. Have seen one unravel on a girls horse at a competitions and the poor bugger flipped over and nearly broke his leg.
They have their place, as MIEventer said, they are good for stables to support injuries. I'll wrap a leg (and the corresponding leg) for short periods of time for injury support, but for anything that is going to need medical attention for over a few days I stick to gauze and elastoplast as polos can cause horrible bruising and tissue damage if left on for extended periods or if wrapped incorrectly.
They are also difficult to put on, if you don't wrap them perfectly, with even pressure the whole way down the wrap you can cause serious injury. Ever seen a bandage bruise? Google it, they're not pretty and take a hell of a lot of effort to clear up.
I stick with boots, neoprene offers a good level of protection, my boots sling under the fetlock for protection and to stop them slipping.
The ONLY time I use bandages while working a horse, is when I am making a sale video or presenting a horse to perpective buyers if the horse is to be sold as a dressage horse. And always white/champagne bandages, simply for appearance, gives them the appearance of having bigger movement.