It's a signal that may be valuable for sites but one that may not have a huge impact on it's own.
I like to have shorter URLs because it ends up being easier and more friendly to share. Longer URLs can be a deterrent. I also like to pay closer attention to the click depth of the page, not just length of the URL.
I'm not sure you'll be hurt by a long URL like:
http://www.yourtld.com/blog/02/08/18/some-crazy-long-slug-nested-with-dates-that-triggers-moz-errors
I would bet you can get that page ranked if the content is valuable enough, even with a longer URL. But the issues start to pop up If you have a site that has content only found by browsing the nested pages it is a larger issue.
For example:
http://yourtold.com/services/cleaning/windows/indoors
This is an example where I'm really worried about the length, but more importantly the overall structure of the URL and site. It may be difficult users, and crawlers to find this content making it less search friendly overall when the content is 4-5 layers deep.
