Agree. You can think of it as a tool inside of SAM. It is built in, but like mprobus stated, you will need other tools in order to unlock its full potential. For example, I monitor our Exchange environment pretty closely with Appstack. This is how some of the products we run fit together for that "single pane of glass".
SAM - monitors the databases and services
NPM - monitors the health of the servers and the network
SRM - monitors our SAN (latencys, IO trending, etc.) to detect issues
VMAN - deep down virtual host and machine monitoring
DPA - I shift it around to certain databases that have issues. I don't really use it all the time.
When you look at Appstack is shows the status of all these on one page so that you can tell where an issue is coming from very quickly. If you do not have these products then you won't see the status of them, but you will still have appstack usage if you have SAM.
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