I am writing this from my July 4th week's vacation (which explains my lack of posts this week).
It's important that everyone on your team gets the appropriate downtime, a chance to recharge their batteries. There were times in my career where I described myself as 7/24/364 (I took Xmas day off!). In retrospect, my productivity at times waned, and I would have been more productive in general if I had taken a week off a few times a year.
Downtime is important for technologists, especially those who are typically on call 24/7. If your teams don't want to take the time, force them. Schedule time off well in advance so projects and deliverables can be scheduled around vacation time. And downtime is about being ready to jump back into the thick of projects full force, recharged!