Apart from the obvious and already mentioned benefits of leaning you better give this subject some thought if you want to reach anywhere near the range/duration as quoted per book.
Of course is leaning easier with an EGT but in a fixed pitch machine you can just:
1. set the revs as per the power you desire
2. slowly lean the engine until the development of rough running
3. enrich slightly.
As long as your power is set at less than 75% there is no chance of doing any damage. (See the Textron site for this)
I think the reason why most instructors don't tell pupils on how to lean is...........................................because they don't know how to it properly themselves.
FD
Advantages of leaning are: Less fuel consumption; less lead deposits in the plugs; less valve stem problems; less engine wear; longer range; saving money etc