hengine | A 2D graphic engine for javascript/typescript | Graphics library

It's in the form closing event, which, okay, yes, if you're building a single form application will also be when the program closes but I think is probably meant to be illustrative of the general principle that you clean up after you're done using things.

You're right in general that if the program's about to exit, you don't need to do such tidying. As Raymond Chen puts it:

The building is being demolished. Don’t bother sweeping the floor and emptying the trash cans and erasing the whiteboards. And don’t line up at the exit to the building so everybody can move their in/out magnet to out. All you’re doing is making the demolition team wait for you to finish these pointless housecleaning tasks.

OS handles will be reclaimed when the process exits. However, if you're communicating with external hardware, it may be cleaner to delete the handles if this places the hardware back into a known-good state (this does beg the question of what's meant to happen if your program crashes however)