It is very handy if there are no third party monitoring tools available/installed to monitor SQL instance performance. It collects and generates reports of data collected. It has some pre-defined data collection sets and can have customized sets to collect the needed. Below are some usecases,
Performance Monitoring and Tuning: Collect performance data such as CPU, Disk I/O, Memory Usage, etc. Use this data to identify and troubleshoot performance issues, optimize query performance, balance SQL Server loads, and for capacity planning.
Disk Space Usage Monitoring: Monitor database and log file size growth, manage space effectively and plan for future disk space requirements.
Monitoring Server Activity: Collect data about user activity, SQL Server instance resources usage, and server operating conditions.
Collecting Query Statistics: Identify costly queries, long-running queries, and tune them for better performance.
Baseline Collection: Collect data over time to establish a baseline for the SQL Server instance for comparison with future performance.
Security Auditing: Keep track of changes in server activity and query statistics for auditing and compliance reasons.
This has good read of it, but based on 2008 version though.