I travel a lot for business, and so am fortunate enough to have reached an "elite" frequent flyer level. There are some well-documented benefits which are common to most of the frequent flyer programs, even when booking cheap economy tickets, such as:
More miles earnt
...and so on (details of course vary airline to airline)
However, what non-obvious or poorly documented benefits are there? For example, I've also noticed the following "undocumented" benefits:
I've been rebooked on competitive airlines when flights have been delayed/cancelled.
Flight attendants/airline staff are (sometimes) politer and more helpful.
(A big one) Exit seats, and other desirable seats, are available for booking as soon as tickets are booked (although most airlines list this as a benefit, it's not always obvious that more seats open up the higher the "elite" level).
Complimentary upgrades when flights are overbooked.
Is there anything I'm missing... that I could be expecting or asking for, and I'm not getting?