Some executives still have their assistants print out emails and/or presentations. Recently, I saw a proposal for a major project sitting on a desk for review, printed in black and white. Colours that looked bright on screen were translated into depressing dark grey and black shades. Big captions in light colours were faded and hardly readable. Photos enhanced with artistic filters looked distorted.
Lesson: try out how your document looks when printed. You can even do that using a print preview, no need to waste trees here. This is especially important if your document contains a lot of text, the temptation to print it is bigger.