Websites that still use underscores for their URLs are becoming scarcer and scarcer. Some say that people who still use underscores are “old school” while dashes seem be used far more often these days.
A usability related reason for using dashes rather than underscores is the elimination of the confusion created between a space and an underscore when the URL is viewed as a link, or when printing such a URL.
More to the point, the chances that a combination of keywords contained in your Web site is included in the SERPs increase exponentially when using dashes.
For exemple: a URL that contains “seo_techniques” will be shown by the search engine only if the user searches for seo_techniques (this kind of search is rarely performed); whereas searches for “seo”, “techniques”, or “seo techniques” gives your URL containing “seo-techniques” a better chance of being displayed on the SERPs. The dash will help you more than you can imagine, by greatly improving your visibility on the Web.
Good argument for dashes. But let me give you an argument against them.
Dashes aren’t natural. Search engines don’t read them. They’re not a part of your keyword so there’s no real benefit. But the most compelling argument against dashes is that there are people who will just type your URL into their browser. They most likely won’t remember your dashes.
Let’s be honest. People are creatures of habit. Most websites don’t have dashes. Why should yours?
Well, to answer the question, you could include dashes to make your long URL more readable. I could have used dashes for www.search-engine-optimization-journal.com. The search engines would have loved it. For one thing, each keyword is distinguishable from other. If you have an URL that could easily be confused for keywords not relevant to your site then a dash might actually be imperative – you know, the break up the keywords and make them more distinguishable. But I didn’t have that problem so I didn’t feel dashes were necessary.
It really is a personal preference. Some people like them, some people don’t. It makes the URL easier to read for humans and doesn’t hurt the spiders. But dashes are harder to remember for humans who type in URLs. The SEO benefits between the two are the same. No difference. So when it comes to dashes, you decide.