Why am I telling you all this? Because in my head, it pays to be as thoughtful about your PTO as your cash. Time, as they say, is money. Those three weeks I carry over not only could come in handy if I need a big chunk of time off, but also as a bit of a financial cushion should I get laid off (which could come in handy, as severance at my company is minimal).
Keeping an eye on my PTO is even more important since I'm in a long-distance relationship. For our situation, since I have more time off than he does, I'll go visit him more often this year. This allows him to bank his PTO and use money saved from travel costs to put towards debt and/or emergency savings. Below is quickie calendar I came up with to help visualize my PTO time, and for us to use to coordinate our visits.
So this is what I've drafted so far, which leaves me 5 days to play around with if I get sick, an emergency,etc. However since I already have 3 weeks that I'll be carrying over, these 5 days must be taken before the end of the year or be forfeited.
I realize that as a single person with no children or other dependents, hoarding PTO time is easier for me to do than others. Even so, I believe that if at all possible, like with having a cushion of emergency cash, we should all have at least a day or two of PTO to be flexible with.