I'm on research leave at the moment and have been surprised at the discrepancies in leave practises between Universities. I'm fairly junior and had assumed that my colleagues elsewhere would have benefited from fairly regular periods in which to finish up papers, put major bids in and basically to put things in place to keep their research going until the next period of leave. However, I have professor friends who have never had a University-funded teaching relief, and other colleagues who have to fight in competitive schemes to claim a semester away from teaching and admin.
Where I am, these one-semester periods of leave are essential as the teaching/admin load is prohibitively heavy to make any real research headway. They come around pretty much automatically every three years or so (with an accepted internal proposal), although since they don't come with funding, it does mean that my departmental colleagues have to cover the gaps left by the one who's on leave. We just get used to permanently being a person down. I also competed for matching funding from elsewhere so I've got a full year. 
I'm loving my research leave so far - time to spend on just one or two projects per day instead of trying to shoehorn bits of analysis or writing into half days here and there (if I'm lucky). I was feeling pretty burnt out with my teaching - taking shortcuts and getting impatient with students who needed my time, so the way I see it, research leaves have many advantages - not just the obviously research related ones. It's also meant I've been able to travel away from my University city so it really feels like all the administration and other time-sucks are far far away.
And I realise I'm very lucky, since leave is by no means a standard across my institution, the UK or beyond. This recent THE article is an interesting survey: www.timeshighereducation.com/features/sabbaticals-no-longer-so-open-ended-or-available/2019616.article
I was going to post on the life passing you by thread www.mumsnet.com/Talk/academics_corner/2499175-Anyone-feel-like-life-is-passing-them-by-due-to-being-an-academic, and realised that what I had to say was dramatically different to how I would have contributed to the thread just three months ago when I was in the thick of teaching and admin. My hours are about a third shorter yet I’m getting much more of value done.
That was long. How does leave work where you are? And any tips for making the most of it?