Let's define "taxiing" as any time your engine is running below 1500 RPM.  Why is this useful?  If your piston engine airplane is equipped with an oil pressure regulated "Hobbs" (counts time when the engine is running) and a tachometer that also records the time the engine is operating above 1500 RPM, you can calculate taxi time as a percentage of engine operation time.  You can then figure out if it is worth the effort to pay attention during this phase of operation.

 

If you fly a C172, with a slow cruise speed (relative to the canonical Lancair 320 speed), a very small percentage of engine time is spent in taxi      since it takes so long to get anywhere.  On the other hand, a very high cruise speed Lancair spends a large percentage of chronological engine time in taxi since so little time is spent in traveling from airport to airport. 

 

For me, approximately 15% of engine operational time is spent below 1500 RPM ((Hobbs - Tach)/Hobbs). What's yours?  Especially Legacy and IV-P people. 

 

To me, 15% to 20% makes it really worthwhile to operate the engine properly and, like many others, I aggressively lean during the taxi phase - generally, the big pull to a known visual position of the mixture knob, to be fine tuned when time is available.  I do this shortly after engine start and as I pull off the runway after landing (assuming I am able to leave the runway under power).  If it matters, the placard on the mixture knob (Push Mixture Rich) has been thumbed to an almost unreadable state.  I may have to placard that placard as inoperable.