From a practical perspective it doesn't take away any freedom. I try to avoid buying any ebooks I can't get DRM free copies of in case the DRM scheme they use changes or goes away and requires me to purchase a new license.

Obviously I could just use the free copy to begin with but it wouldn't send any information to the people that make such books that I want more of them. Also the QA on such books can be a little light and format shifting them is a hassle I do if need be but would rather avoid.