1. if you're rockin' vintage track parts, they're square.
2. if you're repurposing 80s road parts, they're square.
3. if you're looking for a completely functional, high quality 3-piece crankset that doesn't cost you an arm and a leg just because some jackass at Shimano thought it would be a good idea to introuce a pricey new and not necessarily better standard, then square it is!