I requested this in the company I used to work for. I was (genuinely) sick, I had bronchitis, which laid me up for a few days of my annual leave. It also prevented me from travelling on prepaid nonrefundable tickets. I claimed on my insurance for the tickets, and was refunded, and I claimed the days back from my employer.
The insurance paid out without a murmur, HR needed a bit of persuasion, but eventually the leave was credited back to me.