I can’t give you a clear use case just yet. Sorry.
But have you looked closely to see where that guide went? It hadn’t much to do with the endpoint on the other object. (although that endpoint may popup ocasionally).
You are pulling a guide from an edge that bounds two connected faces. If for some (stupid?) reason the side face seems to have more focus, the guide ends up in its plane. If not, it end up in the front face’s plane.
If you want it to always end up in the front face’s plane (say in case of a closeup view) why not keep it constrained th that face’s plane by temporarily holding down [Shift]. No way it ends up elswhere. I don’t see the “relevance” of the endpoint on the other object.
In some cases, say when pulling the guide outside the front box’s area you get SketchUp to ignore both planes (side and front) so the guide end up in the red/blue plane of that particular endpoint. You’ll then see a red dotted line running from that point. And a thin arrow running from source edge towards guide in progress. Holding down [Shift] will lock the new guide’s position to the red/blue plane of the obstructed endpoint.
Use case? it’s up to you, right now it’s not that clear to me. But that endpoint plays a minor role.
Added: the minute you see your guide disappear, hit [k] to get all backedges visible. SketchUp now shows that the gude is pulled along the side face, indicating so with a green arrow instead of the red arrow for the front face.