With FA2 NFT tokens, is it necessary to implement the permissions_descriptor? As far as I can see in tzkt, it doesn't look like it's actually being used. Are there any contracts that are actually used?
You can see the tzip-12 specifications for FA2 contracts. https://gitlab.com/tezos/tzip/-/blob/master/proposals/tzip-12/tzip-12.md#fa2-transfer-permission-policies-and-configuration
There is no strict standard on permission policies for FA2.