Why not? Surely if its a final its better to have a result rather than someone win based on who scored more in the first innings or something
I may need to double check but have the ICC just suggested a "timeless test match" only 2 weeks after banning runners ?
I just think that with the 5 day test, teams know that they have 5 days to win, lose or draw so it adds some urgency to the games, especially on days 4 and 5. Without a 'time' limit, the game will just go through the motions untill someone wins, with no real excitement as you know that someone has to win, whereas with a game that has a time limit you don't know if it will be a win, loss or draw.