I know the problems associated with TPG’s, but I like having my cards slabbed for protection and the registry is a great way to catalog a PC in my opinion. I like doing research and adding new sets and items too.
Being the only set listed on the 82 Topps Blackless registry with maybe 15% complete led to a longtime collector contacting me and selling me a full set. Good luck finding one of those in the wild anytime soon. Picked up an 85 Minis and Desert Shield set from the same contact.
I agree with a previous post about connections made in the registry too. For most of my sets I have contacts of folks that collect similar stuff, and most of those contacts came from being on the registry. I have met some other cool people that share similar collecting goals on boards like Net54 and Facebook too. It is fun helping each other track down stuff. I would have never found some of the tough items in many of my sets without help from other collectors.
I could care less about grade for my Mantles or oddball sets. I sold all of my PSA 7 or higher Mantle base cards a few years ago. I have fun scanning and saving the slab images too. To me, flipping through my digital collection brings the same enjoyment as flipping through my physical albums. I am not wrapped up in the registry by any means, but I do enjoy some aspects.
It’s a hobby…to each their own

Happy collecting!