Instead of adding a "hide" option in user settings, have you considered making the sidebar toggleable with a button instead?
Advantages of a togglable sidebar:
- Site maintains a consistent look and feel between users.
- More intuitive than searching through settings menus1.
- Doesn't require changing site-specific preferences on each community.
- Guests can hide/show the sidebar without needing to login.
- Fewer preferences help keep the options menu simple.
1Currently, disabling the sidebar involves navigating through User Profile → Edit Profile & Settings → Preferences → Navigation → Hide left navigation.