Pressure on the moving foot might help control a beginner's poorly aimed movement, but with good aim it is wholly unecessary.
As for being able to lift the moving foot off the floor to prove balance. Well, first it doesn't prove balance unless you can stay in that position. Certainly there is a point in each step where (if you were not already moving) you could hold the position indefinitely - you are balanced. But during most of the duration of the step, you are not balanced, for the simple reason that your body weight is not over your only standing foot. It doesn't matter if you lift the moving foot or keep it on the floor - as long as it is not supporting your body weight, it cannot contribute to the physics of your balance.
What a little moving foot pressure could do though is contribute to your SENSE of balance - it uses one of your five senses (touch) to give you feedback to improve your aim, but it does not actually contribute to supporting your body. Again, beginners need that, experienced and well practiced dancers usually aim well enough that they don't need these after the fact corrections unless something unexpected happens.