This is a great tool to analyze your Lync deployment and should be leveraged on a daily/weekly basis as part of your Lync Server operational best practices. The BPA will scan your Lync infrastructure, report errors, warnings and information about the settings and configuration.
The BPA validates your Lync infrastructure versus a list of our Lync Best Practice configurations, hotfixes, service packs, etc maintained by the Lync team. We update the list of best practices frequently as configurations, hotfixes, best practices evolve. The Exchange 2010 built-in BPA is another great tool to provide the same functionality against your Exchange 2010 infrastructure.
The Lync Server 2010 BPA can be downloaded here.
The Lync BPA TechNet documentation is here.