Well for a start the best way to use them is as a feild ops and use it to call in artillery strikes, Which can lead to killing sprees. Other ways to use them are:
Mark out danger points with covert ops
and use them to find other feild ops and kill them aswell as any other type of class.
Either way you use them is fine. Best maps to use artillery strikes on are flat maps as then you can see exactly where to send it to.