On the -800 we usually have the nr. 1 recirc fan off below FL100, on the -700 the only one, only downside is slightly higher fuel burn. Makes for a much less noisy cockpit environment. Thank god the good ol' standby altimeter vibrator is not an issue anymore with the ISFD, that was kinda annoying and some CPTs pulled the CB for that which i never really liked as there is a reason for the vibrator, however noisy it is.