Gluing-technique tips:
For the strongest possible bond, especially with epoxy and porous surfaces (balsa, plywood, some 3D prints), consider adding a thin scrim of glue to both surfaces when practical. It's common to apply glue to one surface and expect it to wet the second surface adequately when assembled but that doesn't always occur.
As many others have pointed out...how often have you had the glue grab too quickly, leaving the coupler/engine block only partly inserted? Epoxy is slower but doesn't grab the way that most wood glues do, so gluing couplers, motor mounts etc. can be easier with epoxy than with wood glue. And with very thin body tubes (e.g. my Saturn V Skylab) epoxy may be heavier, but there's no solvent to evaporate so epoxy avoids distortions in the tube that can occur from water evaporation with wood glues.
(Yes, I'm an epoxy fan.)