I acknowledge that some people think that limiting a service is just an exercise in covering the controller's 6, but if you know that the picture is not as good or complete as it should be you need to tell the pilot. If you don't, you are leaving yourself wide open. It is negligent to mis-lead the pilot into thinking that the controller can see everything out there. Getting a radar service does not mean that the controller can protect the pilot from everything. Limiting the service reminds that pilot of that part of the contract you may not be able to fulfill. A lot of pilots do not know what their responsibilities are when in receipt of a radar service, nor the conditions that apply to the service.Similarly, reminding the pilot of his responsibilities with respect to terrain clearance when working at the MSFL or SSA is necessary as a lot of pilots don't know what their responsibilities are!
As for limiting a FIS - total hoop!
JSP 552 235.125.1 FIS is a non-radar service provided, either separately or in conjunction with other services, for the purpose of supplying information useful for the safe and efficient conduct of flight. Under a FIS the following conditions apply:
a. Provision of the service includes information about weather, changes of serviceability of facilities, conditions at aerodromes and any other information pertinent to safety.
b. The controller may attempt to identify the flight for monitoring and co-ordination purposes only. Such identification does not imply that a radar service is being provided or that the controller will continuously monitor the flight. Pilots must be left in no doubt that they are not receiving a radar service.
c. Controllers are not responsible for separating or sequencing aircraft.
d. Where a controller suspects, from whatever source, that a flight is in dangerous proximity to another aircraft, a warning is to be issued to the pilot. It is accepted this information may be incomplete and the controller cannot assume responsibility for its issuance at all times or for its accuracy.