In Parelli Natural Horsemanship, we're not allowed to voice cue at all, from day one, because we need to develop our body language, & skills with giving the right feel with rope & stick/wand to the horse. It's a discipline that will improve your clarity for the horse tremendously!
Also, we understand that going round & round in mindless circles is totally boring for the horse, so we keep it short, & keep it interesting by causing changes of gait & direction & allowing the horse to pick the direction sometimes, in a spirit of amiability, & not facing him with "all your eyes" (your entire front, solar plexus, etc., facing him "sounds" like a bullhorn to him), but standing STILL & passing rope behind our backs as he goes round. We allow him to "ask a question", we don't get on him for breaking gait or anything, so as to keep the relationship top priority, not his perfect performance.
In short, I don't longe, I do circling game, for the reasons mentioned.