• everyone knows what's happening, because requests are accessible by all support staff
• the turnaround of customer requests is faster, yielding improved efficiency
• request tracking, escalation and workflow is improved
• better information is available in the form of online access to:
• Known Errors, solutions and request histories
• external knowledge sources
• management information is more accessible and accurate
• duplicate, lost or forgotten requests are eliminated
• skilled staff and resources are better used
• complex support tasks and calculations are made easier.

Source: ITIL Service Management, Section 4.3.2