I have two bikes with pedals that are spd one side and platform the other. One is the TCR that is loaned out to casual riders and is my Long ride bike. I change the pedals to SPD's only when I ride it as I do not like not being clipped in. The other is the beater and is the bike I just jump on for local trips. Platform on one side and any shoe will do- including Crocs. Only thing I notice is that the firmer the sole of the shoe on this bike- The less foot pain I get.

For cycling you do need a firm sole and nothing better than a specific cycling shoe to get the right amount of firmness.