Many different factors can affect the state of the artwork, such as stress cracks that cause paintings to flake over time or humidity that creates blotched areas. ... Although preserving art is costly and time-consuming, it's important because you are saving cultural heritage for future generations.”
conservation for art is "preserving, fixing, or just restoring old art or other things like artifacts etc." (found in an article on www.msaconservation.com) it's most likely controversial because if something's old and valuable, people want to keep it in it's original form. (just a guess) but that's how it is in the art world.
