Nothing, zero, zilch. They get paid well and the service is rarely up to that in the US. Just don't do it.
Getting a bit O/T here, but now that USA tipping has come up, yes, the wages in the USA are generally very poor, especially in the hospitality industry, compared to ours.
Some workers don't even receive the minimum Federal wage, of $ 7.25 per hour, and they might only be required for four hours on the night.
That's right, it's not $17.00 or $27.00 per hour, and a few States have even lower levels than $7.25 per hour, and they can get split shifts with no guarantee of actual hours to be worked.
How many in Australia could survive on the minimum USA wage? Not me that's for sure.
Also, the IRS deems that the worker has received a certain amount in tips, which is assessable as income.
Regarding service in restaurants, Australia generally needs a awake. When was that last time that ice water arrived as you sat down, the food options on offer was fully and expertly explained, the wait-person had all right answers and drinks were never empty?
I've pretty much always found that most of the Yanks were right on the ball. If for no other reason that to get those tips.
If it's an allround poor experience and you aren't suitably impressed, it's a different matter.
Of a number of trips to the USA, there would only have been several average experiences in restaurants.