no float couse problems sprinting or result in problems with knee pain because the foot, knee and hips are forced to be in one single position, usually not a natural position anyways. I havent used shimano pedals ever, nor spd stuff... but i had used the old looks, the 1st generation and was a pain in the ass use them. I used them for 1 week, untill TIME came up to the market with a double security system plus floating plus bioposition...since then I havent moved from TIME. Time was the reason why Look came up with floating systems too, Shimano and campy had to do the same.

People do not realize sometimes the difference between a natural pedaling and a forced one because of no float cleats... well are their knees not mine...

cya good luck