Many players on this server have friends (If you don't you must be weird :/) and most players want to see when they were online but we have no access to ./seen I believe if you lift this command to everyone people will have the ability to know if their friend came online when they asked or if their friend has quit the server. So yeah..
essentials, however it only works per-world - if they hadn't logged into tg1 for weeks, and you executed the command in tg1, it would give a couple of weeks. It would, however, work in the hub, since everyone who logs in goes through the hub.
./seen is an admin function. The reason for this is because the /seen command allows you to see when a user last logged in, and their IP Address, which is and should always be confidential information.
it is possible to only have the last logged on feature, as there's the normal permission, and the admin permission for it