XV valves are usually on/off type of valves. These valves may be solenoid operated (Whenever they are used in ESD interlocks) or manual valves. They are used basically for providing tight shut off (TSO) conditions.
Control valves on the other hand, as is clear from the name itself, are used for controlling the flow based on the process conditions.
Suppose, you have to maintain a certain level (Say 50%) in a vessel. For this you need a control valve in the pump discharge at the bottom of the vessel. If the vessel level increases beyond 50%, the LIC of the vessel will open the LV in the pump discharge so as to maintain the level in the vessel. This type of controlling is not possible by XV.