This question is related to a previously asked question of mine about adding accidentals.
I often pencil in fingering in difficult places, but sometimes I even mark fingering on an entire piece (in order to help me play it). But unlike marking the accidentals, this habit does not seem to be as problematic because it might improve one's ability to process information while playing (one needs to pay attention at the same time to the notes and the fingering).
So, should I limit penciling in fingering to trouble spots, or should I just freely mark fingering as I wish?