Imagine you're a marketer and build a campaign to make people visit your website. How can you prove that people visited the link because of your campaign? That's where UTMs (Urchin Tracking Module)  come into the picture: these parameters (added to links) don't affect the page you see, but they allow marketers to measure their campaign's efficiency by tracking where you came from and what you did inside their website. In other words, a simple way to stalk you.