Piranha allready said, but what i like to add:
If you echo loads of code (with <br />'s in it) it looks great in Dreamweaver
But if someone visits your page, and he looks at the Source, all the HTML code is in 1 big line in a total mess 🙂
So \n is a good way to make your html-source nice and tidy
its like an [ENTER] when editing your HTML-files in wordpad.