where they are used
A half lap "joint" is used to join two pieces, usually at 90 degrees/right angles They are used in doors or gates where ever strength is needed. They are glued together and typically do not require additional fasteners or dowels, but that's not problematic if you choose to dowel them.
If you are making a door, put up a diagram or sketch of your plans for addition comments and advice. :smile3:
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)