Can I add another reason here - I’ve struggled mentally as I’ve gotten fitter with the absolute numbers. There’s something about doing a particular number of watts that’s really intimidating, even if it’s a workout I’ve done before, just with a different FTP (and therefore wattage).
Having the option of putting everything in %FTP would remove that intimidation factor of doing a wattage number I’ve never done before. Instead, I’d being seeing the same workout as I’ve done previous. It may seem small, but I can make a big difference.