Then again, the Doctor also needs tricorders for scanning his patients.
He's not integrated to the ship's sensors so thoroughly that he would have "supernatural" senses. He wasn't intended to, because he was supposed to be mere rush hour help. A medical tricorder obviously sees something in the patients that the general room surveillance sensors cannot see. The handheld holographic camera could also see things that the room sensors cannot.
It is something of a mystery why we don't see more cameras, or fewer cameras. If away teams cannot pipe up any visual data except when one team member has a headset or wears a rigged VISOR, why aren't headsets and VISORs mandatory for all away teams? OTOH, if visual imagery can be recorded by tricorders (and we see this at times), why the headset in "Identity Crisis"?
I would suggest that tricorders usually record sufficient visuals, but specialist cameras are used for a more "dramatic" recording - one where the angles and framings are chosen by a dedicated visual recordist who holds the recorder at eye level. The devices used for this dramatic recording are then equipped with a variety of drama-enhancing bells and whistles; civilian ones, like EMH's camera or Chakotay's "tourist" disguise one, have more of those for the sales appeal, while professional journalists (ST:GEN) or Starfleet officers on assignment ("Identity Crisis") use more austere and compact gear.
Timo Saloniemi