“The difference between pornography and erotica is lighting.” ~Gloria Leonard
There is really no way to light a subject worse than with direct flash.
Much of the time, beginner photographers don’t have any knowledge about their camera at all, and in particular they have no idea how to light something. Their cameras are usually set to “Green Box” (sometimes labeled “auto”) mode, which is fully automated. In addition to taking over most of the menu settings, this full-auto mode also pops up the on-camera flash when there isn’t, in the opinion of the camera, enough light.
I’ll grant you that the little flash that’s built into the top of many digital SLRs has probably made the difference between getting something and getting nothing, but I’ll also say that in my entire career, I’ve never seen an image I loved that was made with direct on-camera flash.
In my day-to-day news shooting, I carry two flashes. I typically put one on the hot shoe of my camera, which has a movable head so I can bounce the light off a wall or ceiling, and the other on a tiny tripod, which I can set somewhere or have someone (like a reporter) hold. The flash on the tripod has a small device called a slave, which fires the flash when it detects another flash, like the one from my camera. For as little effort and weight as this setup has, it can make a huge difference.
The game-changer recently is that the newest digital SLR camera have super-clean high ISOs available, such that you can almost shoot in total darkness. Thus, the pop-up flash is just about out of a job.