Something I've been thinking about, for quite some time now. If you work evenings or weekends, you're more likely to use a couple of hours PTO here and there for various events. Maybe it's a family gathering on a Saturday, maybe it's your kid's recital on a Wednesday night, or maybe it's a concert. This creates a disparity.
These events are scheduled for the 9 to 5 crowd, so they don't miss work. The 9 to 5, Monday through Friday crowd can take a vacation AND attend these events. Meanwhile, those who work evenings and weekends, have to decide between going to their nephew's birthday party on a Saturday afternoon, and taking a nice, long, and deserved vacation.
I don't think it's too much to ask for a couple of extra hours of PTO a month if your schedule requires you to work nontraditonal hours.