In a year when I was flying to the US a lot, the mile-multiplier my status gave me got me extra business upgrades equivalent to an additional $10k or so of ticket costs (alternatively I could've taken lots of free flights). They also got me free premium economy upgrades on every flight, priority boarding etc.
The mile-multipliers were nice.. however from what I found the quickest way to get miles was to use your personal card to get reimbursed for work things.
Since I was UK based and primarily flying United that wasn't an easy option for me unfortunately (I did have a British Airways AmEx. though). But regularly flying London<->San Francisco got me up the tiers very rapidly anyway.
