In Germany it's somewhat "optional", as the tip is supposed to represent how happy you've been with the service and there's legislature in place that specifically states that tips are not supposed to be part of the wage. But that also depends on the service you are using. A small tip can also go a long way of making you a preferred customer: At my favorite Thai place I sometimes round up what I pay by 50 cent, in return I get a free serving of spring rolls (worth 2,50€) with every order, making the 50 cent investment a rather good deal ;)