One of the most invidious policies around when I was leaving in 2003 was that 'leave carry forward' was limited to 14 days - anything more was 'at Stn Cdr's discretion'.... Which was rarely granted.
So, overstretched folk who hadn't been able to take their leave due to 'operational tempo' simply lost it - because the Stn Cdrs would be 'looked upon unfavourably' if they started approving carry forward of the real amount of lost leave.
I think it's the Canadians who allow you to carry forward all lost leave to your exit date - which can lead to quite a figure when a senior officer carries forward all the leave he lost as a JO! And is now
paid as a senior officer....
Personally I always thought that any refused leave passes for any particular year should be returned to the applicant. At the end of the year, any lost leave could either be carried forward in perpetuity (so if you lost a week in 2003 and another week in 2004, you could carry forward 2 weeks to 2005 as you wished), or paid for by a day's pay per day lost. Because if you weren't able to take leave, you were obviously doing someone else's job as well as your own and should therefore be paid for it.