When I got my DSLR, I had a terrible need to check my photos really had quality (framing, composition, focus, noise, colors, etc.), it was then that I realized the possibility of reviewing this quality through microstock platforms, since these companies have rigorous assessment criteria. In many cases the sales of images for those platforms are not always interesting, but for me it did fit, served as a mechanism for quality test my work. It is important if you have no interest in staying using microstocks for marketing your work, be aware, once you have proof of their quality, do not be sending more and more images to be evaluated without the interest of keeping them for sale.
Obs .: remember, if you have not interest in participating in the marketing of their work through these mechanisms, use your work without much value, just to check if you have enough techniques to ensure quality work. After approval of his work at microstock, delete the image sent for evaluation and feel confident that you have enough quality to produce good work.