On systems prior to XP the Task Scheduler was only a convenience for users and could be safely disabled. This is no longer true. Disabling this service on XP or Vista will have serious consequences, although this will not be immediately obvious.

These systems schedule a number of system maintenance tasks to run every 3 days. Without the Task Scheduler these will not run. More importantly, Windows will be unable to add to, update, or delete files in the prefetch folder. Prefetch will be effectively crippled, leading to impaired boot and application launch times. Over time this may become severe.

Users must be very careful when disabling services. Microsoft documentation is not complete, many services do more than stated. Months after disabling service a new application or device may not work properly. A user will not likely connect this failure with a disabled service. In any event the benefits of disabling services is highly overrated.

Larry Miller
Microsoft MCSA