Kobi:
If you don't have a copy of the D7i manual, or the 3600HS(D) manual, or the 5600HS(D) manual, they can be downloaded from Minolta USA's web site.
Here is a link, which discusses the limitations of the internal flash:
http://www.arnason.no/modules.php?op=modload&name=Forums&file=viewtopic&topic=23&forum=2
If you compare the internal flash with an external flash, and the subject is less than 10 feet away from the camera, you probably will not notice any difference, unless the light from the external flash was bounced off the ceiling or the flash was used on a flash bracket. Some flash brackets will allow you to keep the flash always on top of the camera, even when the flash is in portrait position. Other flash brackets go a step further and ensure the flash is oriented with the CCD/LCD in addition to keeping the flash on top of the camera.
The primary advantage of keeping the flash on top of the camera is to prevent heavy one-sided shadows when a background is close to the subject. Shadows won't necessarily be eliminated, but will be even on both sides, and less noticeable. Using an external flash in bounce mode helps even further in reducing side shadows, and provides a more natural lighting effect.
Keeping the flash oriented with the CCD/LCD will prevent parts of the image from being underexposed; e.g., as when flash is in this position --- , but the CCD/LCD is in this position ~ . In other words, the LCD, CCD, and flash head are not square ...... they are rectangular.
William