Page rank for your website can become incredibly important in terms of effecting your business' marketing and bottom line. If you have a lower page rank or get your page indexed / crawled slower, your site will not come up in search engines as often and traffic will suffer. If you link to a lot of external sites, especially those of questionable content or quality (which is hard to always be aware of), Google and other search engines will lower your site's rank at least to an extent. If you have many links on your site, it might even delay the indexing or crawling of your site so that search engines won't have the information as quickly and your content will take longer to appear on search engines.
So does this mean you should use the "nofollow" tag/code on all of the links on your site? Of course not. You still want the crawlers and spiders to follow your internal links and links to your other website content. In many cases, if you are advertising a link to someone else's site and you are being compensated, they usually expect you to allow following for those links. It is not as big of a deal to skip the nofollow designation when it comes to reputable websites, especially as a favor or virtual vote of confidence. If you want to make sure your site doesn't get dragged down by your external links, it's a quick and easy way to help out. I'm not saying these tactics will put your site on page 1 of Google, but every little bit helps these days in an increasingly competitive internet world.
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Frugal Business Internet Marketing