Many search engine marketers have historically recommended placing relevant keywords in URLs. The original rationale was that a URL's contents are one of the major criteria in search engine ranking.
Over time, this has changed. It is now a less important criterion with regard to search engine ranking. On top of that, dynamic sites make employing such URLs more difficult. That does not mean, however, that creating such URLs with relevant keywords is obsolete and unnecessary! So let's enumerate all of the benefits of placing keywords in URLs:
Doing so still has a small beneficial effect on search engine ranking in and of itself.
The URL is roughly 20% of the real estate you get in a SERP result. It functions as a call to action and increases perceived relevance.
The URL appears in the status bar of a browser when the mouse hovers over anchor text that references it. Again - it functions as a call to action and increases perceived relevance.
Keyword-based URLs tend to be easier to remember than ?product_id=5&category_id=2. Read : Using mod_rewrite to optimize URL
