I was reading another question on the site when I noticed the EVA suit sports heels.
Why do they put heels on space suits? (cropped detailed view)
That only looks like a heel! As shown here, it's a "foot restraint interface"!
That said, it probably makes walking around in the training facilities a lot easier. Although that doesn't happen much - the EMUs are heavy.
Source: JSC-19450 Rev. B Extravehicular Mobility Unit Systems Training Workbook
This picture of a Manipulator Foot Restraint - it was grappled by the shuttle robot arm and used to move crewpersons around - shows the interface with the boot. You can see where the heels fit.
Source: Smithsonian Air & Space museum
And here's a crewperson in the restraint.
Finally, here's the Portable Foot Restraint attached to the space station robot arm. You can see it has the same interface to the boot.