Front Brakes Hardly Working

When replacing front linings ( most common service required )
it's common practice to just close the calipers with a clamp, pushing contaminated fluid backward in the system, including the master cylinder. That can damage one half of the master cylinder.
You wouldn't need to jack the car up to prove me right or wrong.

This causes more harm than most will ever know. You push contaminates back into the Master cylinder bore. You can ruin the rubber cups or clog the discharge port causing the brakes to lock up. Really is a no no to push the pistons back in without the bleeder open.