This picture from early in the game shows how cloisters tend to flock together during the game, since they are one of the few pieces which contain field on most of the sides (the meeples here have been moved to show the cloisters that they're on).
Usually when a cloister tile is pulled, the player tries to find a place to put it that is already mostly surrounded by tiles, for a faster score. This tends to be around cloisters that have already been placed. Here, the person lucky enough to pull a cloister tile with one road coming off it will be able to play it in the empty space in the middle for an extra fast score!
