Hi, it is explained in the wiki:
https://wiki.openstreetmap.org/wiki/Proposal:Public_Transport
https://wiki.openstreetmap.org/wiki/ES:Tag:public_transport=platform
https://wiki.openstreetmap.org/wiki/ES:Tag:highway=bus_stop
https://wiki.openstreetmap.org/wiki/Tag:bus=yes

It is made to understand the type of public transport, for unification and also fixing errors with validators.

In this case I could have added these references in the changeset.

I hope I have explained it well.

Regards