Off the top of my head;
- Approving/disapproving threads/posts
- Revoking warnings
- Warning users
etc..
For 1: These are logged in Moderator Logs.
ACP link: /index.php?module=tools-modlog
MCP Link: /modcp.php
For 2 and 3 we have a separate log called User Warning Log. Go to ACP>Tools & Maintenance>Logs>User Warning Log. (Address: /index.php?module=tools-warninglog)