One of the most important items to watch for is an overloaded MWG device. The number of requests per sec (req/sec) is a good indication of a box that is undersized and overused.
This screen shows the req/sec at 92. This means that over the last minute the average req/sec was 92. Along with a line graph showing the previous req/sec. In this case it was pretty consistant.
If you need a longer stretch of time or more details, the best screen to gather this from is the Requests Per Protocol screen.
On this screen we see a fairly busy server running approximately at 450 req/sec.
220,000 - HTTP + 50,000 HTTPS = 270,000 total for 600 seconds (10 minute Resolution). 270,000 / 600 = 450 req/sec
Notice this chart from the same server from basically the same time frame. It only shows ~250 req/sec (15,000 / 60), which is very different than the 450 req/sec listed above.
Reason: The executive summary screen only shows good/blocked sites. Things in the whitelist, or auth bypass, etc.. Do not count towards this graph.