If you want to keep your website fresh and up to date, Updates can be a wonderful tool. In most cases, simply updating your home page can do the trick. Sometimes, a new photo will help or new content may be even better.
If the site is strictly educational, fairly deep, and the technology unchanging, updating can be unnecessary.
If your home page is a newsletter, frequent updating on a monthly basis can be a great idea, as long as you are consistent. A monthly newsletter can be a great way to attract a loyal clientel as long as there is substance to your content and you are very consistant with your update frequency.
Sometimes, data can get stale, especially if it appears to be old. Depending on the situation, it might be best not to put items on your website that could be out of date soon. For example, it might be better to have clients call for your most current price list, rather than constantly updating them.
The bottom line is don't let your website become stale. Learn what content can lead to this and avoid it at all costs unless you are committed to frequent updates.