The css rule above has nothing to do with what tags you use as you are just describing a base font size for the document. The p tag will inherit that font-size automatically (see your other post as I explain why you should use percentage font-sizes anyway).
What you intend doing (not using p tags) is very bad practice as all content in an html document must be in the appropriate tag to satisfy all manner of devices.
If you have a paragraph then use a p element as that is what it is designed for and is the semantically correct element to use. A lot of devices are semantically driven (search engines, screen readers, accessibility tools, human readers) and all look at the html document to decide what's important and what is not important which they do by looking at the tags that you have used. (It is also invalid to have inline elements as direct children of the body in some doctypes).
A documents structure must be complete and exact and describe the document as semantically correctly as possible. Notwithstanding the above the actual process of doing this invariably leads to better and more easily maintained and stylable documents by the simple act of having it described correctly from the start.
Never skimp on semantics
If you don't use a p tag then what do you do when you want a new paragraph? Breaks are not meant to create new paragraphs and can't easily be styled and should never be used just to make space.