Warning

• JoinEdge does not fill any gaps between surfaces. When surfaces won't Join, that's an indication that more time should be spent fixing the gap/overlap/other problem so they WILL join.
• If the surface edges are not close to each other, you may have problems later on, depending on what you do with the model.
• If you cannot join surfaces using the Join command, you should make the surfaces more accurate.
• If you use JoinEdge, you should learn what it does and use good judgment. Try to think of it as a shortcut for changing your tolerance to a bigger value, doing a Join, and resetting the tolerance.