They switched to this combined PTO system at my husband's workplace shortly before he was hired. They used to just let people take as many sick days as they needed, but people started abusing the system. Since so many of the employees there have been working there for 10+ years and have tons of vacation time and their kids are all grown, they didn't mind. Most of them had more PTO banked than they could use.
But new hires, like my husband and most of the people in his group, get screwed. They get 10 days PTO for the first 4 years & that has to account for vacation & sick days. What ends up happening is that the younger folks go to work sick, especially in the beginning of the year, because they have to save up the sick & vacation days for if they really, really need them.
For example, my husband went into work sick today because the entire workplace has to take a mandatory holiday from Dec. 24 through Jan. 2. If you have PTO to use on those days, great. If not, too bad! And if you have customers who need work done during that time? Too bad! We are a large, inflexible company! We do not accommodate the petty requests of individual departments, no matter how profitable they are!