Clearing Unnecessary Services (2)
Although services don’t necessarily use any processing cycles unless an application makes a request and you can’t easily remove them to recover the hard drive space they use, services do use memory that you can recover. Because services can become very large and memory is a precious commodity, removing the services you don’t need is a good idea.
You need to consider the ramifications of removing some services, but disabling others is a no brainer. For example, disabling the Messenger service (not related to Windows Messenger) is a no brainer because this service has been linked to a number of viruses and few people seem to use it, even on those large corporate networks. However, you wouldn’t want to disable the Internet Connection Firewall (ICF) / Internet Connection Sharing (ICS) service unless you have a third party firewall and don’t need to share your Internet connection with anyone. Unfortunately, running a firewall is going to slow your online game—you have to make a choice between a secure connection and a fast connection.
NOTE It’s possible that a service you didn’t need in the past suddenly becomes necessary after an update. For example, Windows Update version 4 will scan your system and download updates to it without having either the Automatic Updates or Background Intelligent Transfer Service services started. However, once you upgrade to Windows Update version 5 (an automatic update when you install Windows XP Service Pack 2) these two services become mandatory because Microsoft checks for them. Windows Update will complain when you try to access it without the services started. To ensure your system can remain updated and yet not use precious resources needlessly, you can keep these two services set to manual and only start them when you want to perform an update of your system.
Taken From : Microsoft Windows XP Power Optimization