I think it can be useful for a horse who is focused outward when the handler is either doing online ground work, or even in the saddle. It's about getting the horse to give up his insistence that he can find comfort somewhere outside of the round pen, or away from the handler, and bring his focus back to the handler, so that it's "accessible". Some horses need to be really pushed to make them give up that outward focus, (though there are likely other ways to achieve this).
But, I think doing it with every horse , just because it's there, is pointless. Do you really have to run a horse around until he's exhausted and begging to get him to pay attention to you?
Most horses will not move around the pen very long before they want to be with you. Heck, they want to be with you before you even send them away, but working on being able to both send them away and draw them back can help them be better focused on you, and you better able to be constantly aware of where your horse is focused, and being able to keep your horse "with" you, mentally.