A leak down test is a really good test. You hear nothing your good to go. Means everything "as far a compression" is ok.
Air coming out the valve cover, means, air is getting by the rings and needs to be rebuilt.
Air coming out the water jackets, means bad head gasket.
Air coming out the intake, means bad intake valves.
Air coming out the exhaust means bad exhaust valves.
None of these test, check for bearing wear and or other failures or problems ie oil pump, water pump. But i think its a better overall test, then a simple compression test.
I know alot of people ding the 3.0 but if rebuilt property can be a good motor.