Quite a few civil spamcans have a high wing configuration. This means that the lookout view inside the turn is degraded whenever the aircraft banks. Hence a prolonged continuous turn from climb out to downwind or from downwind to final is undesirable as it would reduce the ability to maintain a safe lookout. However, not a problem in low-wing military trainers. Whereas quick turns in a 'square' circuit get the blind spots over with quicker. You can still fly tight circuits even if they're square. Personlly, though, I'd far prefer to fly 'military' circuits within gliding range of the runway as far as possible!!