Record Arm Buttons on Busses - Why?

Hi,

Quick question - since the manual doesn't seem to cover this and chatGPT etc. jut spout unfathomable nonsense in response to this, so...

Why is it that Submix / Return / Output busses all have Record Arm buttons?
- I've not found them to have any useful function, so I'm a bit stumped...

Thanks in advance for any light cast on this.
J.