Originally Posted by Bacciagalupe

Data from pedal-based power meters makes it very clear that you apply very little useable force on the upstroke when clipped in. You aren't applying power throughout the entire pedal stroke; what you're doing is pushing down, and then getting your leg out of the way. I.e. a bicycle operates like a two-stroke engine.

Clipless does not:
• Significantly increase power output
• Fix crappy pedaling technique
• Make it physically easier to climb

The benefits of clipless are:
• Improved control
• Staying attached to the pedals when applying lots of power (e.g. sprinting)
• Encourage riders to use stiff-soled bike shoes
• Improved ride feel

Clipless doesn't cause any real harm, and offers useful advantages for many riders. But it's still not the case that you are applying force in "four directions."