That si better than running the drives 24/7 - if one is going to go then that way it is more likely to go alone. If every in an array (anything I even half way care about get s the RAID1 or RAID5 treatment) has been spinning for years then a power cycle can be quite scary. Restarting once month or so increases the chance that if they fail they'll not all fail at the same time.

Having said that, my main little server at home hasn't had a power cycle for somewhat longer than a month as there have been no kernel updates or that like that have required it...