Choose http or https during the manual installation of WordPress and the database

When you install WordPress manually, somewhere during the process, it asks you to select the weather in which your site uses http or https. Why is this? Does matters? How will your choice be translated into changes / a different use of, for example, your database?
When I installed WP, ​​I chose http bc at the time I did not have an SSL yet. Then I created a few pages, posts and categories. The URLs of these started w / http.
Then, a while later I installed the SSL certificate in that domain name and since then pages, publications …

Choose http or https during the manual installation of WordPress and the database