Ear Worm: "Call Mr. Plow, that's my name/That name again is Mr. Plow".
Family-Unfriendly Aesop: The moral is "Starting a competing business is being a jerk" or maybe "If you have a friend with a business, you can't be a real friend if you start competing with him" and maybe also "Stealing ideas is wrong", but in real life, competition is a key factor in our free market and it's good for the customers (who Homer shows nothing but contempt for, incidentally). Also, there are cases of people who are business competitors but still friends, like Bill Gates and Steve Jobs. Plus the law says you can't own ideas and many people agree. Barney was shown as clearly wrong on shooting out the tires of Homer's plow and making a defaming commercial against Homer, but the aspect of competing with a friend is debatable.
Also, Homer, by trying to get Barney to stop, puts Barney's life in danger. Homer saves him and only then does Barney agree to stop the competition and be partners, but Homer conveniently doesn't tell Barney he was responsible for this, furthering the moral that two friends can't have both competing businesses and stating that if you put someone's life in danger and then save them, it's not necessary to tell that you made the problem in the first place.
Harsher in Hindsight: Homer (as a teenager) ruined Barney's life by giving him beer the night before his SATs, and before Barney became a drunk, he was an honors student with his sights set for Harvard University. And if that's not depressing enough, watch Barney's short film on "A Star is Burns" about how his alcoholism has ruined his life.