I'm an "exempt" employee. That means that I'm exempt from the fair labor laws. It means that, for example, I don't get docked in pay if I work a few less hours this week. It means I don't punch a timeclock. We just had a bit of a big deal about this at work. Some of us were taking parts of days off, and marking them as such in our system: "I took two hours off today." HR told us to stop. Apparently, there's some kind…
It would depend on company policy. If company policy requires you to take PTO for a doctor's or dentists appointment, then I'd only work 40 hours at that company.
If the company doesn't account for exempt time, then they may get more than 40 hours of work out of me.
Regarding exempt employees having to take PTO, recent court challenges in California have come out in favor of the employer. See Rhea V. General Atomics. http://caselaw.findlaw.com/ca-court-of-appeal/1673316.html