Pi Zero Micro USB to USB A is a really useful USB specification! It allows some small devices that would normally be unable to act as a host to have limited hosting capabilities! Pi Zero Micro USB to USB A is great for things like tablet computers and smartphones in order to allow for USB peripherals like flash drives, keyboards, etc. to be hooked up.
Not all devices are compatible, so make sure that whatever you’re plugging in actually has this ability so you don’t damage something!