ditusa,
Thanks for that link. Now there is one on the list.
To build a speaker cabinet without it doesn't make sense.
1. Stronger joint for structure integrity.
2. More bonding surface than traditional 45 miter.
3. Provides an air tight seal.
When I purchased my first locking miter bit I purchased it at Woodcraft. I figured I would ask the staff there as the majority that work there are seasoned woodworkers who have a shop.
None of them had experience with it nor could advise.
Personally, I would not build a cabinet without this joint.