Drupal will load unnecessary entities (non-node) if a menu link to them is in the main menu. The reason I say it's loading them unnecessarily has to do with the fact that if a menu item is disabled it will still do an entity_load on it.
How to repo:
Standard Drupal Install
Create a new user
Link to user/2 in Main menu (admin/structure/menu/manage/main-menu)
Disable that link in the menu.
user/2 is still loaded on every page load even though that menu item is disabled.