Ok I understand now
Its just that I readed "Edges" while thinking about lines and not solids
So I thought it was the same thing than the join command

Its good to repair models indeed, so when you make a fillet to that box there's no extra edge :)

Thanks for the explanation

When you say:

In the future at some point it should also get applied to curves and surfaces as well, as a way to merge 2 curves into a single curve segment, or 2 surfaces into a single surface. That's unlike Join which glues things together but results in a segmented (for curves) or multi-surface (for surfaces) object which can be broken back into its individual parts with Separate after that.

You mean it will be possible to do a boolean union using surfaces instead of solids ?
That sounds awesome !