It's great for experimenting with startup applications. The SCU main interface contains several tabs that allow users to selectively and non-permanently alter several startup parameters. The first two, SYSTEM.INI and WIN.INI, are included for the purpose of legacy compatibility; there's very little chance you'll ever need to tweak them.
The BOOT.INI tab lets you play with the file that defines how Windows XP boots. The entire file is displayed in a text box in which you can select individual lines, which in turn you may be able to alter through checkboxes, but there's little advantage in doing so unless you're troubleshooting something.
The Services tab lets you check and uncheck XP services, but there's a better way to go about enabling and disabling them that we'll get to later.
Under the Startup tab, you'll find a listing of each program that's called to start after Windows XP is booted up. It's here that you can disable things that you suspect are unnecessary, such as Microsoft Office's TSR, Quicken Agent, launchers employed by multimedia programs like RealPlayer and WinAmp, and other such nonsense. The beauty of the SCU is that disabled items aren't permanently deleted: you can uncheck particular components, reboot, and then test your applications and hardware. If you determine that something has ceased to function, you can fire the SCU back up, recheck the box next to the startup item in question, and reboot.
You can often improve system performance vastly by experimenting with the SCU and eliminating everything that isn't absolutely necessary. Once you've determined a particular startup item to be useless, you can purge it from wherever it's being called by checking its location in the SCU listing. Items shown to be in "Common Startup" are called through the Start Menu's Startup group--delete their icons and they won't be launched anymore.
