Default WordPress URL structure i.e. permalink structure is not considered as SEO friendly. Search engine likes permalinks with post name as slug in them.
SEO friendly URL structure increases your chance of better ranking on search engines like Google etc. Likewise search engines are the largest source of traffic to popular blogs and organic traffic also gives you better ad revenue.
A SEO friendly URL structure is a user-friendly URL structure in which a visitor can know where he is going to simply by looking at the URL. This also works for search engines as well.
Continue reading How To Use SEO Friendly URL Structure In WordPress?