A single fraudulent grade could in practice make the difference; a series of them certainly could. In this case some other, presumably honest student who would otherwise have gotten the scholarship, admission or job has been wronged. And the higher the level, the greater the wrong, from the plagiarized intro-course essay to the term paper to a masters and doctoral dissertation. The misrepresentation gets you on the bench, and somewhere in the end, in the dark, somebody falls off.
Taken from an excellent webpage called "ACADEMIC PLAGIARISM DEFINED" by Professor Irving Hexham. U. of Calgary.
Now, at the beginning of the semester, is a good time for faculty and students to talk about plagiarism. This website also gives lots of examples of original, plagiarized and properly cited information.
I've also got a site "Plagiarism--A Guide for Instructors" that might be useful for deciding why, when and how plagiarism affects both students and faculty. The University licenses a utility called Turnitin to help detect plagiarism. It's an instrument, sometimes a useful tool, for detection, but does it teach students to think or does it just challenge them to defeat the instrument. The best strategy for both students and instructors is to head it off; design assignments that can't be plagiarized. Takes time, takes thought, takes attention. Being original is hard--on both sides of the desk.