I've shifted without the clutch in standard cars (synchro type transmission), on motorcycles (dog type transmission) and in a nice little racecar with a motorcycle engine & gearbox.
Transmissions with dogs instead of synchros handle clutchless shifting quickly and efficiently, at the expense of noise and jerkiness. (Yes,
Jerk is an actual engineering term).
With a synchro box, clutchless shifting is slower than using the clutch, and much more likely to damage the transmission.
I don't see the benefit to clutchless shifting with synchros. Sometimes I will ease the car out of gear without using the clutch, but not back into gear. My tranny has 218k on the ticker and it's not getting any younger!