To give more xp and gold to the remaining players, are there any cases of a player disconnecting as a deliberate strategy? That is, a strategy that is planned beforehand, not a rage quit or fulfilling a pub request to "uninstall dota". And if so, is it allowed in tournament play?
Having played a game on a team with 3 disconnects (perhaps rage quits over stealing farm or something equally trivial, in any case I didn't see it), and then the two of us that were remaining could quickly buy strong items and won the game against the five remaining opponents. This was a low skill match, but I imagine similar could happen in higher skill arenas.
Note that it would still be possible for the remaining players to control the abandoned hero, so they're not completely out of the game, and they could even continue, for example, farming for more gold for the team. It would require someone with the skill to control both their own hero and the abandoned one, but controlling multiple heroes is not uncommon in Dota2 (e.g. Lone Druid or Meepo). The redistributed gold could be enough to give the team a significant edge, buying some more expensive items sooner.