I don't know why here in the west it's common practice to actually not pay employees enough and rely entirely on tips. Without those tips, many job offers in the service industry would not be attractive, as they don't pay enough to make a living. Without tips, many of those positions never could be filled, unless wages were raised.
Of course, if wages were raised, the increased cost would ultimately have to be passed on to the consumer. So instead of paying €9 for your order, and placing a €1 tip - you might end up being billed €10 instead. At the bottom line, on average, this would work out to the consumer paying the same with or without tips, and the worker earning the same, with or without tips.
But with tips, that's just the average - while in actuality, some patrons will tip a lot more than others. And some workers might earn a lot more tips than others.
If you assume that workers are unfriendly by default, you could see this as an incentive to make them behave more friendly in an attempt to earn a tip. If you assume that workers are friendly by default, you could see that as a green-light for them to be unfriendly to those customers who don't tip. Not sure if creating a competitive environment between your workers is a good thing...
What tipping does, is make things more uneven. Some customer will pay more, some customer will pay less, some workers will earn more, some workers will pay less, some patrons will be treated more friendly, other patrons will be treated less friendly. The average stays the same, but the variance increases.
Without tipping, things would be more even. Individual cases would stay closer to the average.