Free Gradings at certain levels. Read about the Benefits here: http://www.pcgs.com/setregistry/benefits.html
My registry sets are at NGC, not PCGS, but one benefit of having them at either site is the ability to share them with your friends and family, if their eyes haven't rolled back in their heads! I've moved so much that I have friends across the country, so when I want to share a particular coin, I can use the registry pictures even when not at my own computer.
In your case i definitely see why you do it! I love coins and sharing them with friends/family is something i do as well. Thank you
There are two benefits, really: 1.) Sharing your collection easily with your friends. I only participate in teh NGC registry, because they accept both NGC and PCGS coins. Since much of what I buy is NGC, I want to be able to post those. The NGC registry allows you to track your set progress, share pictures, organize your set, and share a description of your coins. If you are feeling ambitious, there are a lot of really cool things you can do. It is a great place to learn about other people's collecting interests as well. To me, this is the primary benefit of either registry. 2.) There is a certain amount of pride and bragging rights associated with the registry Competition. I don't know what the PCGS site does, but NGC mails out certificates to the best sets in each category each year - and if you are one of the winners of their registry-wide competitions (best set, best classic set, best presented set, etc.), you get a really cool plaque. I won #1 Best Presented Set in 2008 for my Franklin Half collection - one of the highlights of my collecting career. I still proudly display that award on my wall.
Easy tracking of the pcgs coins you have , easy way to shop for the coins you need. Can be made for private or public viewing.
To be honest, I think the populations are also more plentiful for PCGS given any specific coin or grade. If you are grading raw coins, economics of submission costs between NGC and PCGS could come into play. If you are buying coins that are already graded - I think you have more luck finding them in PCGS. I started with NGC and am building my only "for show" set with them of MS64 grade Peace Dollars. Plus I'm an avid contrarian - and since everyone is on the PCGS bandwagon - I'm not. Another benefit is insurance coverage in case of theft. Also, a database of your coin collection is always nice to have - and approximate value.
I use NGC Registry Sets because they accept both PCGS and NGC slabbed coins. PCGS accepts ONLY PCGS slabbed coins. So you would have to buy ONLY PCGS slabbed coins OR do crossovers (spend more money). As for the benefits of NGC Registry Sets, as others have said it's a good way of showing your coins. AND it's easier to do that. Instead of loading one coin at a time I can just copy/paste the link and the job is done. That may be a case of overkill sometimes (if I want to show just one Classic Head half cent I end up showing them all) but it's quickly done. EXAMPLE (if I get this right): Here's the afore mentioned Classic Head half cents. https://coins.www.collectors-society.com/registry/coins/MySets_Listing.aspx?PeopleSetID=89446