Daily games are different than live games, partly based on how ratings work. I think your rating adjustment is based on the ratings of the two players at the time the game ends, not the ratings at the start of the game. If you think your opponent will have a higher rating in the future, your rating may benefit a little by extending a lost game. This is especially true if your rating is provisional. In some cases your rating benefits from finishing sooner. Chess.com also has the following rules.
Sportsmanship Policy: Do not make your opponents wait unnecessarily.
Fair Play Policy: Do not artificially manipulate ratings.
What are you talking about? In almost every serious chess game people resign when they are clearly lost. There is nothing inherently wrong with playing until checkmate, but it's just a waste of time. Why the hell would you want to play for example a mate with a queen and king for weeks?