I use a compression gauge to phase a camshaft. The higher the compression (after inserting an offset key), is good; if low, insert key the other way. Kind of like a cheap dyno run.

Other than that, it just can only tell you general gross condition of an engine, as stated above.

I do not leak-down test much--if ever--because I can tell the general condition of my engines by oil blow-by. In extreme situations, it fills the dump tank between sessions and leaks out of the seals. Time for a fresh motor. The more oil in the dump tank, the more wear on your rings and cylinder walls.