Permalinks are the permanent URLs of the blog post or page on your WordPress site. Permalinks are also referred on some places to as pretty links.

WordPress automatically enables the default permalink structure after you install WordPress. The number that is used in the default permalink advises WordPress where the content can be found in your database. The default WordPress permalinks or links are similar to this:
http://www.example.com/?p=11

However, you can easily edit their settings and how they look in your browser’s navigation bar by going to Settings > Permalinks option page. Here is an example:
http://www.example.com/2016/08/what-are-wordpress-permalinks/

You can change their format, places, and months and dates, use post names, category and more. We strongly recommend using permalink structures to make sure your website is more SEO friendly, with more data included in there. You can change the structure of your permalinks at any time, however doing this changes the URL of your pages. This can cause your search engine traffic and referral traffic to drop considerably as visitors are presented with 404 page errors instead of the page they wanted to view.

In fact your permalink structure dictates how your website URLs are constructed. From an SEO and performance point of view, there does not seem to be any major benefits to choosing one permalink structure over another. So, it really comes down to your own preference.