While working on a BPMN model, we encountered an issue concerning exception flows. Whenever an exception flow was needed, we gave it its own end event. Although BPMN recommend using gateways to merge normal flow with exception flow. I can see no advantage in doing so, only some additional complications.
However, consider the case in which we have a subprocess with an activity X and an attached-to-boundary non-interrupting event. When triggered, a parallel token will be created and put on the branch of the exception flow. After running through exception flow, an end event consumes this token.
I assume this consumption doesn't trigger the upper-level flow(the one containing this particular subprocess) to continue, as there still is a token left in activity X. As this activity is ended and normal flow is executed , this token is consumed as well and the subprocess doesn't contain any token. This will trigger the upper-level flow to continue. As this is the case, I can't think of any case where the merger of exception flow and normal flow should be necessary. (Except for the one where activities after activity x have to be run in exception flow as well, causing them to be executed multiple times).