I did that twice, once at a dying company when a coworker quit until I lined up a new job in a couple weeks, and another time was a horizontal transfer where two engineering managers were rather vocal about my working solely for them. In both cases I just kinda did what I wanted, knowing there was nothing they could do.
I suspect the question they meant to ask was who was getting paid for two jobs. I have a really boring story about that revolving around a company that paid out severance gradually instead of lump sum, which given the time of year was financially advantageous for me WRT marginal income tax rate.
Here in Japan, where I live, this is one of the reasons that people can't take all their accrued vacation, even when quitting their jobs. When you leave a job, your accrued days are paid out as if you were still working. So if your last day in the office is June 30, but you have 30 days saved, your last day as an employee is ~August 15.
This sometimes means you can't start your new job until after that, and because employers typically want people to start ASAP, people end up forfeiting the vacation time they never got to take while working. The new employer wants them on July 7, so they take just the one week and then start at the new place.
And given how hard it is to take time off, the typical employee has lots and lots of unused PTO. My workplace has a cap of 40 and I am always at the cap.