Screen sharing literally gives you a window into a remote computer, allowing you to see and interact with that computer as if you were sitting in front of it. The window on your system may be part of an application, or it may fill your local screen. Sharing a screen becomes useful in four general cases:
Using remote programs and data: When you need to use a program without transferring the program and/or its related files or data to your local computer.
Technical support: Screen sharing is great for providing remote tech support, whether for your job or to help far flung friends and relatives who rely on you for help with their Macs. (See the case study, below, for an example.)
Headless server access: When you operate one or more servers that are located outside of convenient access, or to which you'd rather not attach a monitor, keyboard, and mouse—so-called headless servers.
Offloading computational tasks: If you have a computer dedicated to long or CPU-intensive processes such as encoding video, you can use screen sharing to check on the progress.
I find screen sharing useful when I'm trying to find an old piece of email and I'm away from my office. My email folder is gigabytes in size, and it changes whenever I send, receive, or file email; syncing isn't a good option, because it would involve transferring too much data back and forth. Screen sharing lets me keep the email on my main machine (my cake) and still be able to search it from anywhere (eat it, too).
CASE STUDY A friend of mine recently switched from Windows to Mac at home with a new iMac running Leopard. He then bought his mother, who lives far away, an iMac. He walked her through setting up iChat, then took control of her computer remotely, set up her email, and showed her how to use iChat with video. In a few minutes, she was seeing her grandchildren on her iMac's screen. You can't beat that for family communication—and tech support.
Screen sharing as a concept is not new to Leopard; however, the solutions included in Leopard tends to be easier to set up and use than many other approaches.
What can you do with screen sharing?
Remotely control the pointer on the other computer: This lets you click, drag, and move the pointer as if you had a mouse plugged into the other computer; all clicks and other mouse operations are sent to the other computer, which then carries them out.
Remotely type on the other system using a keyboard: Anything you can type in the screen-sharing window using your local keyboard is typed or used to carry out commands on the remotely controlled computer.
Copy the contents of the Clipboard back and forth: Anything that you can copy into the Clipboard can be transferred between a remote and local computer, using Leopard's screen-sharing technology or controls built into VNC.
Tip
Screen sharing makes a remote computer "think" that a keyboard and mouse are directly plugged into it, more or less. For local networks, if you want to use a keyboard and mouse on another computer that already has a display, you can turn to Teleport, which lets you shift use of a keyboard and mouse on one computer to others on a network without sharing screens (http://abyssoft.com/software/teleport, donationware).
What can't you do with screen sharing?
Drag files back and forth: While some advanced remote access software programs, such as Timbuktu Pro, allow you to use a file listing to copy files, and even let you drag files to and from a remote system, screen sharing in Leopard is only about remote control. (With Back to My Mac and other file-sharing options, though, you can move files between the local and remote computer, too.)
Use peripherals: You can't use an iSight camera, a hard drive, a scanner, and whatever other peripherals you might have attached to your local computer by the system you're remotely controlling. However, you can use any peripherals on the remote computer from the remote computer. That is, you can print a file from a program running on the remote computer to a printer that the remote system can reach.