The way you save a graphics file for print use and the way you save it for Web use is quite different. You want to find a balance between the size of the file and the screen display quality of the graphic. All readers will be seeing the graphic in much the same way, printed with a certain process onto a certain type of paper. Readers will be seeing the graphic on different platforms, with different browsers, with different monitors. Readers see a reflective image created using subtractive colors.
Readers see a projected or transmissive image created using additive colors.
The viewing experience involves picking up the paper and looking at the graphic. The viewing experience involves the browser contacting the server, the server delivering the graphic across a connection to the browser, and the computer's video card displaying the graphic within the browser.