Mutual Interest is neither directly nor indirectly proportional to the compatibility of the relationship. It is an added benefit that both the people in the relationship have the same interests. They both could do the same things with equal zest and energy and can have conversations about the same things for hours!
Planning activities could become a lot more easy and fun. Having said that it is completely fine to have different interests as long as couples prioritize spending time by merging their interests and participate with equal enthusiasm.