I know the explanation about the usage of RD, that it makes routes from different VRFs globally unique.
AFAIK, a VPN route is composed of
[RD] + [VPN label] + [Prefix]
Isn't the VPN label, that is allocated for each VRF anyway, enough to make the route globally unique?
[VPN label] + [prefix] unique enough?
Is RD used because it's user configurable and allows for more control? unlike VPN labels that are randomly allocated by the router.
Or maybe RD is used - since a VPN label isn't always mapped directly to a VRF (maybe sometimes it's mapped to a route directly, to save a VRF IP lookup when forwarding traffic towards a CE router)