Blocking balls thrown in the dirt is one of the most important things that catchers do. It keeps runners out of scoring position and also keeps double plays in order. A catcher who does a good job blocking balls in the dirt is worth his weight in gold to a baseball team. Catchers should practice blocking EVERY DAY.
For more information about the mechanics of blocking and for more drills check out my book Catching-101: The Complete Guide for Baseball Catchers: