Like most here I let the reader fill in most of the characters physical description. That serves a couple purposes. It involves the reader with your character and makes them far more realistic to the reader. It allows the writer to concentrate on revealing inner character rather than describing ripe melons of the 44 DD variety or the rampant 14 inch battering ram both of which I find somewhat tedious. It also spares you those awkward devices where the narrating character spends time studying themselves in a mirror and then relays their own description to the poor reader.

Just a few drawbacks I can think of. If some characteristic is important to the story you really need to put it in. ( she's gonna be burned as a witch cause she has red hair, He'll never play the violin again because of the tragic accident at the saw mill that turned his right arm into a stump.) Any such tidbits should be mentioned early before the reader begins to envision what the character looks like. For that matter those feeling the urge to describe their protagonist in great detail should do it quickly for the same reason.

just the rambling thoughts of
Mad & Lews