In the past I never used the media library because I wanted totally control of everything and just embedded stuff I had uploaded to specific folders via FTP with html-code into posts and pages.
However, there are more and more themes that force me to make use of the media library, so here I am totally frustrated:
When I upload one image to the media library and the have a look via FTP I see that WordPress had made 11 copies of the image in different sizes and formats. I totally do not understand why this is. If I upload an image with the size 1200x600 I don't see the point of having an unrequested copy in 500x500 or 250x250.
Probably useful to know is that I tried to create a slider for the Customizr-theme, what by the way stretches the images in a unwanted way, but this is another problem.
Thank you very much for you information.