As the aircraft climbs you will need to lean the mixture but not be too aggressive looking to keep the EGT well rich of peak. At above 8000ft a normaly aspirated engine can't make more that 75% power so no damage can be done by the leaning alone but the lower airspeed in the climb and the the reduced ability of the thinner air to cool the engine are good reasons to keep the mixture rich of peak to ensure that the CHT is maintained below 450F.
Initaly in the descent I would not bother to lean off but would start to go towards rich at about 4000 ft.
As long as 75% power is not exceeded lean mixture is not a problem so low power settings are not going to to do any damage.