There really isn't an answer to this question because there's no such thing as "GPSFileDepot maps". GPSFileDepot is just an archive of maps that are made by many different people with different skill levels and interests. So you will see a big variation in the maps on this site.
But you could made some generalizations...
Garmin's 24k topo maps include DEM (Digital Elevation Model) data in their proprietary format that provides 3d shaded terrain. This feature is only available on Garmin products, there are no third party tools for using DEM in a map.
Garmin's 24k maps contain routable roads based on the same data from HERE that is used in their City Navigator products. This means they can provide turn by turn routing instructions to reach a destination. Almost none of the maps at GPSFileDepot are capable of this, they cannot calculate routes.
Garmin's maps also contain a rich database of POI's - things like gas stations, restaurants, stores, etc. Maps on this site are not going to have that level of detail.
Garmin's maps can work seamlessly with each other across state lines. In most cases, maps from different authors at GPSFileDepot will have some issues where they meet.
Garmin will offer tech support for their maps and will "hold your hand" if you have problems installing or using the map. This could be an advantage for people who are not technically inclined.
Garmin's maps are copy protected which severely restricts their use. The downloadable Garmin topo maps can only be used on the original GPS for which they were purchased. So if you sell or lose your GPS, your map will be useless. The maps that Garmin sells on SD cards can be used in any GPS but you must use them on the original SD card, they will not work if copied to another card.