In my own experience, I went to a relatively small church (<200 regulars) that decided to have the contemporary/traditional service. They scheduled the traditional service at 9:30 and the contemporary at 11. As a result, the church self-segregated into two camps that only met between services. As a result, the church was weakened by the lack of fellowship, and many were disaffected and left. Only after they abandoned the split service did they thrive again (and even then, the damage was done).
It’s a danger. It takes good leadership to bridge that gap.