Of course it depends on how the problem is constructed as to wheter or not this is applicable, but yes, the properties of similar triangles are used together with the sine laws (and the Pythagorean theorum) to solve problems. Often these kinds of problems have a triangle constructed inside a similar triangle, neither of which is labeled with enough information to solve a given trigonometry problem. You are expected to find the "missing" information by using the properties of similar triangles.