How do you squegee a shower and bathtub?

I’ve noticed that stores like Bed, Bath and Beyond and Target sell squegees that I assume are for keeping your showers and bathtubs clean. This sounds like a dumb question, but do these things really work? If so, what is the most effective way to use them? Are they really worth the extra effort for keeping your showers clean longer? I don’t mind cleaning the soap scum; that’s easy enough. It’s the buildup of hard mineral deposits that I hate, and I would appreciate anything that would slow down this process.