Removing the user agent (default) CSS from most elements is usually a good idea. This has long been done by "universal" resets or things like the Eric Meyer Reset. I think the best option today is Normalize.css.
One way to explain it is that Normalize does both more and less than a reset. It does more in that it covers more browsers than old school resets did, fixing modern issues as well as legacy issues. It does less in that it leaves styling alone that is already consistent across browsers. For example, it leaves header tags bold because that's already consistant across browsers and is likely something you want to have anyway.