In an old 172 with a carby I would be reluctant to lean the mixture during climb even as per the flight manual unless you were experiencing rough running, which seems unlikely at the sorts of altitudes one would normally fly them.
In the newer fuel injected 172s I would lean as per the flight manual procedure which says above 3000ft providing it is equipped with an all-cylinder monitor (which the new ones are).
If you don't have fuel injection and an all-cylinder monitor, my advice is just burn the extra fuel and put up with the slight performance loss until you're at a cruise power setting.