The main aims of a University are to teach students and to generate new knowledge. These two aims could conflict with each other. For example, when I devote much time and effort for teaching, I might miss these resources for research. An alternative view is that good researchers also make good teachers, because they have a deeper understanding of the problems and this will improve their teaching. The empirical evidence is not conclusive.
It has, of course, implications for the organization of universities, in particular for the incentives related to teaching (typically: none) or to research (typically: somewhat more than for teaching). Some argue that spezialisation is a good way of addressing such conflicting goals, for example, by separating the faculty into "teachers" and "scientists". Others require mandatory teaching training (I have not yet heard of mandatory research training).
Recent research by Aurora García-Gallego, Nikolaso Georgantzís, Joan Martín-Montaner, and Teodosio Pérez-Amaral provide evidence from a Spanish University that
professors with a typical research output are somewhat better teachers than professors with less research. Moreover, non researchers are five times more likely than researchers to be poor teachers. In general, the quality of university-level teaching is positively affected by published research across most levels of research output. (p3)
This does not conflict with my suspicion, but I would like to see more evidence on this. As universities regularly collect students' evaluations of teaching and require staff to provide details on their research, this evidence could be readily provided, for example, as students' term projects.