Lighting objects is a lot like playing pool. Light will bounce off the object and continue on like a pool ball would.
You don't want that light to bounce back into the lens - otherwise it will show up as a big reflection - which is why point and shoot photos taken in museums and any places with glass cases are usually terrible.
When lighting products a good starting point is to light off camera axis in such a way that the light doesn't bounce back into the lens. Often lighting from both sides with large diffused light sources can be the way to go, but there are a lot of different solutions depending on the object etc.
These light tents provide some diffusion but you still have to put the light in the right place. Also they don't do anything you can't do with standard lighting equipment.