What is the use of the 'last seen' devices?

[EddyG]

I have seen that there is a 'last seen' text device created on all of my zigbee2mqtt devices.
What is the use of it?
It looks like it is not updated, the 'Last Seen' field is updated.
How can I get ride of it?

[sammyke007]

I use it to check if all of my Z2M routers and end devices are still connected to the coördinator. Most Aqara/Xiaomi stuff for example checks in every 50 minutes. You need to enable last seen however in the frontend of Z2M.

[EddyG]

What I mean is: what is the difference between the 'last seen' message and the 'Last Seen' field. because they are different.
And why a TEXT device.
I would expect that when I put in the z2m config last_seen: ISO_8601_local that the 'Last Seen' field is updated.