Comment on WordPress SEO Tutorial 2014 Anchor Text by SEO Dave.
In a perfect SEO world you would change the category and post slugs when changing the title of a category or post, but that would require setting up 301 redirects and 301 redirects do cost a little link benefit probably equivalent to the dampening factor (15% of PR/link benefit) associated with linking. If there’s external links to the categories or posts it will cost you some link benefit long term. If there’s only internal links which will automatically change when the slug changes medium term there’s no lost link benefit.
I tend to be lazy and not change the slugs unless they are particularly poor. It’s only one of a lot of SEO factor and if you change a category slug that’s about WordPress SEO from “seo” to “wordpress-seo” the SEO benefit is shared equally over the keywords, leave it as “seo” and the one keyword receives all the SEO benefit, since SEO is a keyword it’s not a loss per se, just means SEO gets all the benefit from that part of the URL. If the category was originally called Stuff and the slug was “stuff” this has no SEO value for the SERPs related to WordPress SEO so there’s more reason to consider changing the slug.
Categories and tags are pretty much identical output wise so I see them as the same thing. Try to avoid adding posts to the same categories/tags every time as it can generate duplicate content issues. If you have ten posts and Search Engine Optimization and add them all to three tags called Search, Engine and Optimization those three tags will have identical content other than the title element, Google will pretty much consider them duplicate. I tend to go for each post goes in one category, in the example above a single category called Search Engine Optimization would have been a better choice. If you have a lot of posts and can create unique categories/tags that have different posts within them by adding posts to more than one category/tag there’s no harm in this as long as all the categories/tags have a chance of generating traffic in their own right. Three tags called Search, Engine and Optimization are targeting HARD single keyword SERPs, no way a tags going to rank well for those single keywords so it would be a waste of link benefit. A category called Search Engine Optimization is also unlikely to rank high for that SERP, that’s competitive as well.
If you can afford to spend the link benefit on indexing pages that are not going to generate traffic in their own right, but will add relevant links to your posts it can make sense to have categories like Search Engine Optimization so they support posts and the home page that have related SERPs to Search Engine Optimization.