I use it alot every-time I compose my posts. It makes it possible for me to generate URLs that provide readers with more information about my posts when scanning search engines results. Atimes, when you fail to use it, Blogger might end up auto-generating a URL that might not really make sense for your blog post.
How To Use Blogger Custom Permalink
To create your own URL for a specific post, go to the Compose page and enter a title for your blog post.
Click on "Links" in the Post Settings box.
Allow Blogger to auto-calculate the permalink. Once completed, click on the 'Custom Permalink" option.
You should see the editable permalink generated by Blogger
Edit it as desired. You can also delete all and retype whatever you want there.
==> Separate each word with -
==> Avoid words like "of", "the", "is", "from" etc
==> The shorter, the better.
==> Each blog post must have a unique permalink.
==> You can't edit permalink of an existing post. It's only for new posts.
I hope this helps.