According to NASA:

The Apollo extravehicular mobility unit was designed to meet a unique set of needs. To assure the maximum return of scientific information from the moon, a method was required for collecting samples, deploying retrieving instruments, and performing experiments on the lunar surface and in free space. Man had to be able to operate safely in free space to provide an emergency mode of translation from the Lunar Module to the Command Module in the event a complete linkup could not be accomplished after lunar lift-off. Since the weight required to provide redundant pressure vessels for each spacecraft would have been prohibitive, a space suit was required.

The website linked to above provides much more detailed information.

Unfortunately, I didn’t check to see if this particular unit was actually used in one of the Appollo missions and if so which one.

Taken with a Sony RX-100 M3.