I use "regular," metal, SPDs for commuting and messing around. I use SLs on the road because good road shoes are drilled for 3-bolt cleats and that's what good road pedals accept (yes, Speedplay, blah, blah). For various reasons, I have regular SPDs on my winter boots, which accept both kinds of cleats, but do not have a pocket for the SPD. That really sucks for walking.