Last week in San Antonio and staying at a Hilton where free breakfast was provided. I was given vouchers for each day saying "breakfast is on us" and underneath "Gratuity not included". So for me and my wife the breakfast value was $22.50 each. On the check, the suggested tip was 18%, 22% and 25% of the gross value before the 100% discount was applied.
As the server literally on one day only cleared the plates away, which you could argue is not my service, but preparation for the next customer - $8 minimum suggested tip is excellent pay for the work involved. Yes I am sure they do other tasks as well, but that should be for Hilton to pay them, the service I received was nothing.