The documentary "Saving Banksy" (2017) deals with street artist Banksy's work and the preservation of his public work. More often then not, Banksy's public paintings are either removed or taken down by private art collectors that hope they can sell them for a substantial amount of money.
I have seen two Banksy related documentaries before – the excellent "Exit Through the Gift Shop" from 2010 (YouTube link) and the HBO produced "Banksy Does New York" from 2014 (YouTube link).
After having seen the trailer for "Saving Banksy", I think it will provide the viewers with more material like the one found in "Banksy Does New York". When I watched the latter one, I felt that I wanted to watch so much more, since seeing the struggle between the private collectors of Banksy's work and the established art world was fascinating to observe.