It allows you to play the tile without triggering the enemies' actions. It can be good but i generally only use it if I I can reduce the CD to null before picking it up since there is a cap of 7 CD. Though I have seen a few tiles with free play go just above 7 CD so I'm not sure if there is individual CD limits per tile or if there is a grace limit to allow you to pick up the upgrade if its within a 7~8 max CD