Headshot cropping explained...
To convey your personality, your headshot is all about your looks and your expression - i.e. your headshot is (should be) completely focused on your face. ...which is why I leave some of your hair (top of your head) out in my headshots.
Most often, professional headshots are used in a fairly small format (LinkedIn, Facebook, top of the corner of a resume, etc.) which leaves little room to actually show your expression and hence personality - furthermore, most of the time the headshot is viewed on a small-format screen (phone, tablet, etc.) which reduces the size your headshot (expression) even more.
So, in order to have enough room to actually show your personality in the image, something has to go - and since the information below your chin (what you're wearing) is more important than your hair, I crop the top of your hair out. Not a lot of it - but just enough to make the eyes sit almost directly on the upper third line of the image. Having your eyes placed here in the headshot draws immediate attention to them and - since most of your expression comes from your eyes - this strengthens the look of you and your personality.