This pertains to the Dutch side only as on the French side, there is a different wage paid to servers and the "service charge" is already factored in the menu prices. Typically, one would leave a few dollars to 5% additional on the French side for good service, if so inclined.

Sadly, this topic gets confusing, is beaten to death on occasion and often leaves a sour taste in one's mouth, especially with some of the deceptive practices going on.