Andy Galbraith explains that SQL Server loves RAM:
A frequent complaint we receive comes from a client that has an in-house sysadmin monitoring tool like Microsoft SCOM/SCCM. They turn the tool on and it startsred-alerting because the Windows server hosting SQL Server is at 90%+ used RAM. The sysadmin (or local DBA) logs on to the server and finds that there is 5GB free (~4%), and the sqlservr.exe process is using 120GB of the 128GB on the server!
In my experience, VMware administrators tend to be most hung up about this concept.