It mostly does not really make sense to use it except when swaps come around and in other rare cases if you're no longer a member. I use the shop app to track record purchases but there is also a store function on it and VMP is one of the featured stores. I think it runs through Shopify, so any time VMP adds inventory of any albums, it adds it to the Shop app store.
As a non-member, it allows you to purchase any items marked as "swaps". Also allows you to order most albums in stock that are listed as "join with this record" even if you are not allowed to buy it in the store as a non-member. You pay the full store price though as well as usually pay shipping if you aren't a member. I didn't pay shipping this time, but I'm guessing that's because it's marked as a swap only and they assume you're a member if you are buying a swap...