If your shoes aren’t grippy enough, you slide when you play, and so can’t move properly. If your shoes are too grippy, you can’t slide them across the floor when you move meaning you have to physically lift them up each time you want to move. What you want are shoes that grip, but also slide the "el dente" of shoes. Unfortunately, floors are different, and what is "el dente" on one floor may be "el slippery" on another, or "el glue" on another. Some players adjust to this by having two pairs of shoes, one very grippy (for slippery floors), and one not as grippy (for more normal floors).