Typically reserved for younger players (draft picks, undrafted players. and 2nd/3rd year players) to make their case for the NBA and the G League. Players get the chance to show their skills/development before training camp starts, and also a chance for players without guaranteed contracts to make their case for a contract and roster spot. Only takes a couple of weeks after the draft
Players do get paid, but probably not that much unless they've already signed a contract with a team. For most of its existence nobody really cared about it, but it has picked up in popularity in recent seasons. Wouldn't be surprised if it actually turned a small profit at this point, there were a few sellout games to watch the Spurs' #1 pick Wenbanyama play
The refereeing and coaching is also usually for development (not getting the best refs and coaches), so the actual product isn't great. But a fun way to watch younger players that you've followed in college try to get NBA attention