In general, just keep in mind that it’s not okay to take code from MathWorks products and give it away, whether through MATLAB Answers, the newsgroup, or any other channel. That’s part of the agreement we make with our customers, and it’s also just good manners. It doesn’t make any difference whether it’s for educational or commercial purposes. Regarding small sections of code, please use your own good judgment. Obviously at some point the amount of code could be so small that it doesn’t much matter where it came from. We’re not trying to split hairs. We just want to prevent copying.
The same goes for community-contributed code on the File Exchange. That code comes with an agreement that says if you distribute it, the agreement (license) should travel with it. Please respect that. But the best thing to do is to leave the code in place on the File Exchange where the author put it. That way the author can receive and respond to any feedback about it. Also, the author gets to see accurate download activity, and the downloader is guaranteed to get the latest best version provided by the author. This approach provides the maximum value for the community as a whole.