A small addition is something tjspiel touched on, shoe stiffness. Most clipless shoes have a stiffer soul then regular shoes. This adds to the efficiency of the system, but is also a draw back if you want to walk anywhere.

Half of my bikes have clipless, half are platforms, each serves it purpose.
Learn to track stand and you will have to un-clip half as much. I can usually track stand even the cargo bike for 10 seconds or so (platform pedals). Fixed, which is SPD clipless with no brakes, can have me at a 10 minute light and I'll still be standing on the pedals like a goof.