What Monitoring Server DOES Provide

Overall, reports cover pretty much everything you’d want to know about how good a job your Lync Server’s doing. For example, you can find all of this in Monitoring Server reports:

1. Information about the communication sessions in your organization. That covers VoIP phone calls, IM sessions and conferences.
2. Endpoint information about each session. IP addresses, connection speeds, which Edge Servers were used, etc.
3. Quality measurements for the different types of communications you use (SIP calls, video conferencing, etc.).
4. Activity lists for each user in the organization, by date and/or session type.
5. Reports on Call Admission Control-restricted sessions.
6. Summary of (and details on) calls made to Response Group workflows.
7. Diagnostic reports and troubleshooting information for session failures (including SIP response codes and diagnostic headers).
8. Server Performance reports:  Shows you which servers have had the most problems, using metrics like packet loss, signal degradation, noise, etc.

And a few more.
Many of the Monitoring Server reports are broken up by type, or medium. For example, one report will tell you about IM sessions, broken down by pool. Another will tell you about VoIP calls in the same pool. A third could provide a summary of all communications in that pool.

What Monitoring Server DOES NOT Provide

• The content of a phone call, IM session or conference. That’s the job of Archiving Server.
• Monitoring for the Windows Servers Lync is installed on. It doesn’t cover Windows processes. Use a standard server monitoring tool for that.
• Non-Lync Server application logging. Use a third-party tracking tool to track activity on these.

Microsoft has a Work Smart guide for Monitoring Server here: Lync Server 2010 Monitoring Server Reports Work Smart Guide – Microsoft Download Center
Plenty of information on each report, what it records, and how to make use of the data.