In a lengthy campaign players may miss some sessions or even stop playing for some time. Other players may join at any time.
What are the advantages/drawbacks of having the new players taking over the old characters? Assume that the player is experienced in the game system, but not on that particular campaign.
Would it be valid for a player to use a character only for one session knowing that the owner of that character will be back next session?
I'm interested in answers from the point of view of the players and the GM.