Most photographers don't modify the appearance of their cameras at all. However, you may sometimes see a photographer (typically a professional) with the logos on their camera covered by black tape. Why would they do this? Are they testing exciting new camera models before they're released?
While this could be the case, there are actually quite a few good reasons why some photographers might want to cover their gear in black tape.
Be less conspicuous
The first, and most common reason, is simply that a plain black camera is more discreet than a camera with white or shiny gold markings on it. This is most useful for those photographers who are into street photography. A camera that draws less attention makes it easier to capture candid photos where the subject doesn't realise they are being photographed.
Of course, with a large camera lens, blacking out the logos isn't going to make much difference to how discreet the camera is. But with smaller cameras and lenses, some photographers find it a worthwhile exercise.
Similarly, with wildlife photography, some photographers like to have the camera and lens blacked out (or with larger lenses, covered in a camouflage coat). This makes it less likely that the camera / lens will catch the wildlife's attention, and so there is less chance the wildlife will be scared away by your presence.
Some photographers use black tape on their cameras to reduce the camera's appeal to thieves. Whether this works or not is up for debate – does a thief really look for a Nikon or Canon branded camera and decide they won't bother with a camera that appears to be unbranded?
Probably not, but depending on the way you tape up the camera, it can be made to look quite scruffy, as if it is being held together by the tape.
This still is not likely to deter all thieves. But if you're photographing in a tourist area, thieves are more likely to go after those cameras that are in a good easily re-saleable condition than those that look quite scruffy covered in tape.
Avoid looking like a billboard
A few photographers may tape up their camera simply because they don't like giving free advertising to the company that makes their equipment. This usually goes further than just adding black tape to the camera, these photographers will generally switch out the branded camera strap for an unbranded one. (On a side-note, switching the strap that comes with the camera for a more comfortable one is often a good idea anyway).
The idea behind covering up the camera logos is that if the manufacturer wants you to advertise them, then they should sponsor you. Why give them free advertising?
Avoid gear-geek questions
This reason might seem anti-social, but it can be a valid reason for a busy or professional photographer to cover up the logos on their cameras. Some professionals get quite annoyed by amateur photographers who use the same brand coming up to them and asking them about why they are using model X camera when model Y camera has been released. Or other similar gear / tech related questions.
By hiding the brand of the camera, they are less likely to get questions of this nature. Time spent answering questions is time lost engaging with the subject and capturing photos, so you can understand why a professional photographer might want to avoid being questioned by other photographers.
You might think that a taped up camera would invite more questions about why it was taped up. But in practice many photographers find they receive less questions with their camera's logos taped over then with the logos showing.
In some cases, photographers have found that having their camera covered in matte black tape helps eliminate reflections from the bright logos on the camera. This could be useful when photographing through water or glass, for example photographing fish in an aquarium.
Most modern cameras are built with pretty tight tolerances, and dust, sand etc. getting inside is not usually a problem. However, when working in particularly extreme conditions, such as a desert, some photographers prefer to tape up their cameras just to be sure there are no gaps that any dirt can get inside.
Sports and news photographers may sometimes tape the lens hood to the lens, to avoid it getting knocked off by accident, or when working in a media scrum.
Tape can't protect a camera from much damage, however it can be used to prevent scratching. So long as a removable tape is used, the tape can be peeled off when the time comes to sell the camera, leaving a scratch-free camera that looks pretty much like new.
So, there are quite few reasons why you might want to tape up your camera. Most of these reasons are for pretty niche uses though, so it's not surprising that the majority of people don't tape up their cameras. But at least now you can understand why someone might have black tape all over their camera.