Because of the hours I worked over my career, and my job, my vacation time was always a pain to managers. I worked 11 pm to 7 am for 25 years, and 3 am to 1130 am for my final 13 years. They HAD to have someone cover for me as I was the only one on duty doing my job.
Vacation time off almost always meant disrupting someone who worked normal hours to work the graveyard shift. So most encouraged me to take my vacation in the biggest chunks of time I could so they got those hours off the books, and shortened the disruption to those who had to cover for me.*
First place I worked the preferred way to take vacation was in blocks of a week or more. I took 3 weeks off one time.
Second place I worked it just depended on the manager approving vacations. I really upset the manager when I put in a vacation and put "you pick the week" on the request because I had too much vacation on the books and I was only going to stay home and work around the house so the specific week didn't matter. My reply to him was to show him the 4 previous vacation requests with specific weeks that he rejected.
Final place I worked it they preferred one week chunks, and in the last 4 years for example I wanted Christmas week off, but was "forced" by my boss to take 2 weeks off because I had too much vacation time on the books. But being in California where they HAVE to allow you to carry over vacation from one year to the next, there was a lot of turmoil between Corporate and us, the only of their 64 locations in California. Corporate spent a lot of money on labor law lawyers and 2 years trying to find a way around allowing us to carry over unused vacation. In the midst of that they bought another location in California, and they finally threw in the towel. The 2 California locations now have their own vacation policy that allows vacation carry over, while the other 63 locations it is "use it, or lose it"
* Second place I worked, a woman who worked graveyard shift weekends (Friday night to Saturday morning, Saturday night to Sunday morning) talked the boss into allowing her to take 3 weekends (only) off. She was going to work her 3 week days still. 6 days had to be covered, and their were 6 of us to cover. Simple, right? Well some thought since I worked that shift during the week that I should cover all 6 days. That would have been 27 days straight. Boss called us all in and said he needed each of us to cover one day. I raised my hand and said "I'll do the first day". Boss said "thanks, you can go now". It took an hour for the other 5 folks to work out what day they had to cover.