SoRCon 8 27 Feb - 1 Mar 2015 Basildon UK http://www.sorcon.co.uk Essex Games 27 Jul '15
Sharp corners, such as on squares, show ding, dent, and mis-punches easily.
However, keyflower uses square tiles. Clinic uses rectangles. I think a number of track-laying games use rectangle. It's definitely doable.
Tiles are different to counters. The shape of a tile is (usually) dictated by geometry. Sometimes square, sometimes hexagonal, sometimes other shapes.
Counters aren't inherently dictated. And there are lots of options you see, not just square and circular. A combination of factors matters, including information to be recorded. And at least one more I haven't seen mentioned: clean punch, which often favours circular.