Originally Posted by funfly
In the cruise is some leaning better than no leaning at all?
Short answer, although already covered above ...
Unless you can confidently lean to a mixture setting that avoids dangerously-high internal cylinder pressures and temperatures, with the consequent risks of long-term engine damage or short-term engine failure due to thermal runaway and detonation (and this is a process that necessitates a multi-cylinder engine monitor), then:
a) NO, if you are at 'high' power settings;
b) NO, NO, NO, if you are at 'high' power settings on a big, turbo'd engine; or
c) DEFINITELY YES, if you are at 'low' power settings.
Determining what the relevant values are for 'high' and 'low' power is something that needs the long answer! Study the POH, study the engine manufacturer's operating manual for the model, then read Deakin from start to finish several times in an attempt to understand why the manufacturer's advice should be taken with a pinch of salt!
BTW, the APS course, which is truly excellent if you really want to understand this stuff, is now available on-line for those that don't have the time to travel to GAMI's facility in Ada. (Edited to say that, by taking the course on line you will miss the invaluable experience of 'playing' with the test-rig engine ... where you can establish different engine parameters such as power settings, magneto timing and fuel type, and watch the effect on individual cylinder ICPs, EGTs and CHTs).