Administrator panel gives you following useful information about your current joomla installation in one glimpse:
1) joomla version: It help you to know are you using the latest version of joomla or not. Do upgrade your joomla version , if you don't have the latest version.
2) legacy mode: There are certain joomla extension(components/module/plugin), compatible with joomla 1.0 but not work in joomla 1.4. So , in joomla 1.4 ,they include a plugin "system: legacy" which you can find in going to joomla plugins list, on activating of which you'll be able to use joomla 1.0 compatible extension on your joomla 1.4 version.
3)Quick access menu: IT give access to some most oftenly used menu item. You can find the same thing inside the menu bar too.