Nowadays, many bloggers are trying to optimize their blogs in search engine as well as blogging. I myself also tried some of the techniques that I learned from internet to optimize my site too. Today, I just came across an interesting article about the basic of Search Engine Optimization explained that
Bold text <b>/<strong> is given more weight than ordinary text but not as much as H tags. As much as is reasonable, enclose the search term in bold tags when it appears on the page.
Another article explained that italic (<i>)/emphasic (<em>) tag is also important as well as bold tag.
When mentioning your keywords throughout the page, it’s helpful to put them into italics, bold, or emphasis (<em>) to make sure the search engines know that these words are important.
CSS <span> tags to format text, but search engines don’t have an easy way of determining either of these. Why make the search engines work harder than they need to? Use these basic HTML tags and help yourself (and the engines) out!
How much they will effect in SEO? It is hard to say that those are not really important but they are needed when optimizing the site.