It's not just uncovering technique issues, but the split seconds or more you spend clipping in/out really distract from focusing on the skill at hand. You can't stand on a pedal properly unclipped, ( you have to offset your foot so you don't clip) which makes learning certain skills really difficult, like front wheel lifts. I know personally my body position and cornering have improved since freeing up my foot and knee to point into the turn. Etc. Etc.