I use mine as an all-over-the-face "setting powder" (shade 30). What I find more interesting about this powder is that they deliver a touch of color. For example, I have freckles, a bit of discoloration in my forehead and minor spots resulting from acne. Being said that, I don't use foundation all over my face (I use Diorskin nude at the moment), cause I do also have a very oily skin. So I just apply a thin layer of foundation on my cheeks, chin and central forehead, and then apply concealer where it is needed at that moment. Les Beiges gives me a velvety, uniform finish that I don't achieve with any other setting powder, and that's maybe because of the subtle coloring it delivers. My foundation matches my skin nicely enough without Les Beiges, but the finish with it is exceptional. Then, throughout the day, I do some retouch and again, because of the slight color, it camouflages any imperfection on the foundation because of the extensive wear (I put my makeup at 7:30 in the morning and take it off at 18:00 usually).
I know that some people (specially all the SAs I have encountered so far) claim they are meant to be used as bronzers. In my honest opinion, I don't see the point of using Les Beiges as bronzers when there are specific products for that that work very well, although I can get that you can achieve a very delicate bronzing-effect out of the deeper shades.