Join Date: Aug 2000
Location: Newton Centre, MA, USA
Programs: DL 2MM Gold, AA Plat Pro; Hilton Lifetime Diamond, Bonvoy Lifetime Titanium (via SPG), IHG Plat
Posts: 2,192
I think there are benefits. They are just unstated / unpublished. Like all the FAs and GAs who will know you and personally treat you better. Like the res agent who will see that you have 150k miles and bend the rules. Etc.
P.S. Any letter that says the service on AF is better than DL leads me to wonder if they are in a different universe. IMHO, the FAs on DL stick around for the whole flight. On AF there was no service because the FAs went and hid.