A number of issues indicate that Drupal's core IA could be better, and solutions proposed range from isolated fixes to totally restructuring the admin menu.

At the same time, it is pretty standard that clients need customizations to the default Admin menu structure. It seems a lot of us might be doing the same thing, over-and-over.
To find sustainable solutions, we need your real world experiences.

Do you build Drupal 8 sites for clients?
Do you ever change the admin interface by adding or removing items? Do you replace it?
Are there certain modifications you make to almost all projects?

If so, please tell us your examples and experiences at https://drupal.org/node/2863330