Xunzi_23
Over-provisioning. What’s that? We can go down this rabbit-hole, but simply it is an unformatted partition space to ensure that the controller on the stick has an unused nand cell playground all it’s own for garbage collection and wear-leveling. Some quality sticks already have this hidden from the user. But some may not have it! You may never see a spec for it.
All USB Sticks (except Fakes) should have a non formattable area, it is intended to replace dead or defective cells.
Size a manufacturers secret.
Regarding the question on power saving, all electronic devices last longer when continually powered.
No current surges to cope with no temperature changes.
NVME and SSD are claimed to last longer in data centers than in private devices, above is the reason.
Housekeeping is a separate story, if the devices can not clean up due power off they will eventually
go read only. Some can be rescued, others will be locked in that mode.
Experienced with SSD and USB sticks, up to now not NVME.