It is difficult to bring up the topic of tips without things starting to get heated, but most would probably agree that so long as an employee gets paid a fair wage, a tip is something like a bonus and not a constant expectation.
The service industry in the United States operates in a pretty unique way in that the generosity of customers is supposed to supplement the subpar wage of servers, bar staff, and other types of jobs in the hospitality industry, a rule that just isn't followed by most other countries. However, that isn't to say that other parts of the world don't care about tips. On the contrary, there are plenty of places where it may not be necessary, but it is seen as polite. Workers want to be recognized for their efforts.
This can leave customers not knowing where they stand in terms of international tipping culture when they travel. Nobody enjoys being the awkward tourist, and more than that, not many people want to feel like they are being stingy because they didn't show the level of financial appreciation that their server expected.