On sleep debt, I can give you a very concrete example.
Let's say as a person you need eight hours of sleep, which is on the long side, as most of us need seven hours of sleep, but let's say that you need eight. Because of work, during the weekdays or school days, you can only get six and a half, so you have five days a week where you accumulate an hour and a half of sleep debt. Even if you catch up on weekends are you going to catch up all the hours that you lost during the week? Usually the answer is no, because there are other demands on the weekend, and even if you can sleep in a little bit later, it may be for an hour or two, but certainly it would not be seven or eight hours more sleep that you would get over the weekend.
We're chronically sleep deficient. We don't accumulate sleep. You can't prepare to sleep longer because you know that you won't be sleeping the next 24 hours as much. That, too, doesn't accumulate. There is a limit on how much sleep the brain can produce over a 24-hour period, or in a consolidated sleep episode. It doesn't matter how much we try to cut it or extend it, we can't do that as a preventative measure.
The best we can do is have a regular amount of sleep that is occurring at regular times, that is expected, and of the quality that is hopefully satisfactory to the point that you wake up rested.