We do CPU and Memory only. CPU Optimization helps keep users from overloading the server with a single process more often than not. There are times things happen and the servers just can't quite keep up. It's just basically changing the Priority of the processes so everybody can remain working while the high CPU process chugs along.
Memory optimization doesn't appear to do as much for us usually, but we can tell when it's not working that memory utilization will be higher. We try to get the most from the servers, so for most clients, we notice when WEM stops functioning and there are memory issues.
That's all we use WEM for in our environment at this time as well.