Choosing not to use a CSS reset can really effect your code when you first start coding your site and look at it across browsers and in the long run create more coding hassle. Have you coded a really basic website for one of your assignments before and it looked fine in Chrome, but when you opened it in Safari or Firefox, it had a weird border of padding around it? Many of our beginning coding assignments don’t use a css reset, so some rules from the browser (which vary from browser to browser) are effecting the display of your code.
Every browser has it’s own set of built in CSS that it applies to the site if you haven’t specified otherwise. This is called the user agent stylesheet. You have probably noticed it when you are using Chrome Developer tools and see a greyed out rule in the css that can’t be changed, but it applying to your element.