Having started a TG tournament, I remember the other reason I don't like rated play.  The games are treated for BKR purposes just like any other game, but the strategy is different.  Whereas a gammon makes no difference in a standard one-point game, the whole point of TG is to play for gammons.  Therefore, a player will be willing to lose two games out of three if he can get a gammon in the third.  This will cause his BKR to decline, if he plays the optimal TG strategy.

My unrated TG tourney is still open for entries, and now is a single section of 20 players ;-)