What I meant was that the person who leaned for taxying might forget to reset the mixture for take-off and thus damage the engine by taking off with the mixture excessively lean at full throttle....
BB - I would be wary of describing the technique shown to you for the information of others. 1 minute at weak mixture and 2000 rpm is actually quite taxing for the engine - if someone does that and cooks the engine they won't be best pleased!