Pit Digging - How Often, How Much, How Deep?

"When do you dig a pit?"
"Why are you digging a pit?"
"How often do you dig a pit?"
"Do you dig a pit for every slope?"
"Do you dig a pit every day?"

Questions about snow study pits are likely the most common question from my backcountry ski clients (nudging out, "Where's the bathroom?" by a large margin).  Evan Stevens was one of my instructors for an AMGA Ski Mountain Guide Course and Aspirant Exam, and in this video from Outdoor Research he does a great job explaining the What, Where, When, and Why's of pits.