The standard role’s WordPress users are assigned are: administrator, editor, author, contributer or subscriber based on how much access you want to allow the user.
An administrator has the highest access, able to use all enabled blog features, while a subscriber has the lowest, only able to read and write comments (read more here).
A site admin user is the next level of access, and responsibility, above an administrator.
Your site admin user is the person who has total control of the entire site including:
1. Manage the access and level of responsibility of all users
2. Manage blog features including access to plugins, themes and blog privacy settings
3. Create new users and new blogs
4. Edit posts, pages, comments on any blog
5. Reset passwords
6. Edit and delete any blog
You need to consider carefully what role you assign all users on your site because on shared blogs Administrators are able to remove other users, including other administrators, and editors can delete content. Deciding who and how many users you assign site admin requires the greatest consideration because of their highest access level.
See next: Changing your site defaults