I've seen nothing to suggest this isn't allowed, and if it is it wouldn't normally be advantageous, unless say a beginner like me was given a professional as a partner. Aside from mandatory serves and receives of serves at the beginning of a rally, is one of the players allowed to exit and stand outside the court after any mandatory shots and leave all the shots for their partner?
Yes and no. The play area is not limited to the court itself. The area close to the court is part of it too (there is a precise definition but I don’t know it). And a player could decide to spend most of their time there. But there is also a rule saying that a player should do their best at any time. One could argue that leaving the court to let the best player win for the team is the best thing to do for the team. But that won’t hold with every judge out there.
The rule @Khady alludes to is §16.5.2: While the court is defined in Law §1.1 as the 13.40m x 6.10m area bounded by the outer (doubles) lines, clearly players are allowed to step out of it, for example for a doubles defense down the straight line, recovering after a dive, or to go behind a shuttle lifted to the baseline. So in practice, the area allowed by §16.5.2 is roughly the court mat, which extends 1m behind the baseline and 50cm at the sides nowadays. You are free to stand anywhere on the court mat; the laws do not prescribe any tactics. In reality, you can go to one corner of the net and hold your racket up. You won't be covering much, but contributing at least a little bit.
Another scenario I can think of is if one player got really badly injured and the pair say had over 5 match points at the time. In that case that player might want to avoid hitting shots they didn't have to.
Irrespective of the abovementioned 5 match points, I can tack on another scenario where another player, now on the opposite end is also really badly injured, that is, one player now at each end, and their partners keep playing until the end of the rally. It is important to note, the really bad injury is not severe, as this will invoke other necessary actions.
