Ge-categories, i.e., 2-categorescategores enriched over groupoids (these are 2-categories where the set of morhisms $HOM(a,b)$ has a groupoid structure) seem to be useful in homotopy theory.
Question: What are results in homotopy theory proved using ge-categories?
I am especially interested in ge-categories where 1-morphisms are not invertible. I would also appreciate references.