With the Screen Sharing application open, you can also configure some options using the Preferences dialog box (select Preferences under the Screen Sharing menu). You can choose whether or not screens are scaled to fit if you connect to a Mac with a higher screen resolution. If you choose not to, you’ll need to scroll to see the entire contents of the screen.
Likewise, you can choose whether the screen quality is adapted when working over a slow connection. This can reduce the quality, but typically keeps onscreen movement from being jerky and slow. Alternatively, you can require full screen quality at all times, although with slow connections this may result in choppy movement and a sluggish feel.
You can also choose what information is encrypted when controlling remote Macs. By default only passwords and keystrokes are encrypted. You can choose to encrypt all data, including screen data. This is more secure and prevents someone from observing your screen sharing sessions, but it does require more bandwidth and therefore can result in sluggish performance over slow connections.