5-10 years ago there were plenty of reasons to use props (eVars didn't have pathing capabilities), but as Adobe Analytics has matured over time, most organizations are now reporting pretty exclusively using eVars instead of props. In fact, it used to be a best practice to duplicate all eVar variables into prop variables, but that is no longer recommended, as it creates 2 separate reports for each variable and generally just leads to more confusion.
Because props don't persist, which limits their ability to break down custom events, we only use them for recording variables that are present/available on every single page and click of our site. These are items like site section, sub domain, s-code version, etc... This enables us to build segments based off of these variables without having to use up our limited number of eVars.
Props can also be used if you are only interested in how many times a specific action happens, but you will never be interested tying that action to site performance or conversion events. But 99% of the time, an eVar is going to be the best method for tracking performance on your site.
