By default WordPress puts the exact title of the blog post as its post URL. Have a look here:
What this means is that, if you have a blog post titled: “This post have a very long title that runs for miles”
You will end up with a URL that looks something like:
Long WordPress slugs come with a lot of problems. Most important of them is that long URLs are NOT Search engine friendly.
But your SEO friendly slugs can be generated automatically by the SEO Post Link plugin. This plugin has been developed by keeping in mind all the shortcomings of the default WordPress slug configuration.
You no longer have to think about how good your slug is interms of SEO. This plugin makes it a lot easier for you.