When you install WordPress, the default permalink structure you have is http://example.com/?p=123 . You can retain this structure if having the shortest URL possible is your priority. Else, you need to change this for better SEO.
The most used custom WordPress permalink structure is http://example.com/postname/ . This is OK if your site will have only few pages and posts. When the site grows, this may affect the performance. WordPress specifically advises not to use this structure.
For performance reasons, it is not a good idea to start your permalink structure with the category, tag, author, or postname fields. The reason is that these are text fields, and using them at the beginning of your permalink structure it takes more time for WordPress to distinguish your Post URLs from Page URLs (which always use the text “page slug” as the URL), and to compensate, WordPress stores a lot of extra information in its database (so much that sites with lots of Pages have experienced difficulties). So, it is best to start your permalink structure with a numeric field, such as the year or post ID.
The permalink structure I use is http://example.com/year/month/postname/ . This is good for performance. Also, gives an idea to the user when the post was written. They can also trim the URL like http://example.com/year/month/ or http://example.com/year/ and see archives for that period.
If you write posts daily or write many posts a day like in news websites, then http://example.com/year/month/day/postname is a good structure.
If you want your posts to be timeless, do not include date information and just include the unique post id.
If you like your posts to be aggregated by Google News, it requires to have a unique three digit number in URL. So it will be good to include the post id in the permalink.
Some people are over obsessed with having category name in URL for SEO. But I have seen this affecting blog structure / incompatibility with some plugins. Better to avoid using category names in URL.

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Great assessment and spot on. I agree 100% that you need to include date references in your URL structure on bigger sites that are updated more frequently.
The one problem with just using post id, like you mentioned is that users cannot navigate around the site by tweaking the urls in the address bar – the flat file structure, while good for seo (in many cases), does not allow for educated guesses when looking for specific content.
Hi Bronson,
Yes, permalink structure is only one of the factors in SEO. So, it is not good to be over obsessed with it. Usability should be considered too. I always guess navigate using the URL structure to find favorite content.
Cool tip Ravi. I’ve been using the domain/post-name structure
thankz for the advice.
Mayu, I was also using domain/post-name structure. Then faced issues as ularal.com grew . Now switched all sites to date based url.