They <em>are </em>common <em>because </em><em>..............</em>
The words "boldface" and "italics" are similar to each other because they are used for the <u>prominence"(</u>emphasis)(Some people use it for<u> "</u><em><u>typography"</u></em>) Other than that they are practically styles that are designed for contrasting with normal font (mainly the Roman font/ document) but they are definitely difficult to read sometimes.
