I just observed too many co-workers in my career who had unexpected things come up after they had used up all their sick time and vacation time so I always had some time on the books. No big deal my first 8 working years, but then had kids so needed some time off for them. When they hit adulthood, I needed some time off for an elderly parent.
I'm in California and the law here is you can NEVER lose vacation or PTO time. Your employer had to either let you carry it over, take it off or pay you for it. Never had an employer willing to buy back vacation. You could have up to 1.5 times your annual accrual on the books, so six weeks. On paper the policy was they could assign you time off if you had too much time on the books, but never saw that actually happen. Sick time, was use it or lose it.
A couple of years before I retired they switched to a PTO system. Your vacation AND sick hours now went into one PTO pool. They spent a lot of time and money on lawyers trying to get around it, but that now meant you could not loose sick hours under California law because it was now just PTO. Only restriction we had after PTO went into effect was comp time for working a holiday HAD to be used in the year it was earned. In TV, EVERY holiday was a normal work day, so those days I used first.
Retired now, so not an issue, no paid time off anymore.
I know one thing my wife does NOT miss was the griping from some co-workers about the system used to determine who got priority for holiday time off. She was in a Union position and the company and the union agreed on a system where everyone would get to pick one holiday based on seniority. After everyone picked their first holiday, they would go through everyone for a second, then a third, until all 10 holidays had been covered. She was the most senior person for over 30 years and the ONLY holiday she ever took off was Christmas. Because of how departments were set up, she effectively prevented everyone, including her immediate and next level supervisor from getting Christmas off. Now, mind you, she worked ALL the other holidays. That was the only benefit given to employees for longevity with the company. Company and the Union saw no reason to change the system, because the people complaining loudest and most frequently about not getting Christmas off, all managed to get multiple other holidays off. My wife did offer her last year to take Thanksgiving off instead of Christmas, but the people who would have benefited from that wanted BOTH Thanksgiving and Christmas off, and if THEY took Christmas off, they would have had to work Thanksgiving.