Post labels are an essential part of blogging. Those are the little categories which you can click on that appear below each post. Some blogs go nuts and will have a dozen labels per post, others (like mine) only use one or two labels per post. The reason I only use one label is that google looks at it for keyword SEO, and spamming too many of the same keyword through links and other uses throughout the website is a terrible idea.
Google hates spammers, and links are the first thing google checks when doing SEO on the body of the page. This goes for all links, not just labels, so be careful and use links to send readers to important information without spamming the links and their keywords all over the page.