Best practice for directory structure?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

• 
  Avtar Ram Singh: Hey guys - just a quick question here. Got a few friends with a problem:
  
  The currently directory structure they have is this:
  
  domain.com/category/topics/blog-category/blog-post-url
  
  So I've suggested that the the way to go about this is that domain.com/blog-category/blog-post-url is what they should be doing.
  
  But they're adamant on keeping the sub-directory "topics" in there before the blog category is in, which I'm not sure about. The "topics" directory is exactly that, just a subdir named "topics" which has the rest of the categories within it.
  
  What's the best thing to do from an SEO perspective?

• This answer was selected as Best Community Answer by the Expert Panel

  
  Tony McCreath: It does make the URL unnecessarily long.
  
  If it was a new site I would avoid it. However it is an established site. Changing URLs now would mean you would need to do 301 redirects and would lose a little bit of ranking because of that.
  
  So I'd leave it as is.
  
  Next time the website gets re-built you could think about cleaning up the URL structure.
• 
  Blade S: I would get rid of the "blog-category" as well, and just leave it domain(dot)com/blog-post-url.
  
  Their current structure is way too long and weird, and not SEO or user friendly. It would be too long even for an e-commerce site, not to mention for a simple site or blog.
  
  The best practice is not to have more than 3 categories/sub-categories.
  
  If they won't give up on it, there's nothing you can do. At least you were a good friend and let them know :D.