Linux.com - https://www.linux.com/news/how-easily-purge-unwanted-repositories-linux
After a year of so of working with Ubuntu Linux (or derivative such as Elementary OS), I almost always find myself with a number of repositories from software I may have installed and removed or never really needed in the first place. That means /etc/apt/sources.d can get pretty crowded and the apt update process becomes a bit sluggish. Or worse, repositories can become broken, bringing apt update to halt. Because of this, I try hard to keep those repositories to a minimum.