Another reason to actually talk to somebody, instead of shutting the radio off, is that every type of ATC service (ATSOCAS like Basic, but also services inside CAS) imply an alerting service.
So if you don't respond at the time they expect you to respond (whatever that is, but typically your next announced waypoint) they will start looking for you.
I dont follow.
If you are OCAS and working a frequency you are expected to respond to calls on that frequency. If you are not on the frequency or have "signed off" then there expectation of your doing anything or of them doing anything.
In my example you leave Southampton class D and wave them a goodbye, all the time you continue OCAS no one has any expectation of your talking to them what so ever.
I agree there are some good reasons for talking. These include:
1. AT may warn you before committing some dreadful blunder - straying into airspace, infringing a NOTAM etc., BUT be careful not to rely on them to do so,
2. It is good practice,
3. Rightly or wrongly many feel there is some comfort knowing there is "someone" on the other end of the radio and the radio is working,
4. You may receive traffic information that could be useful,
5. You might receive other information that could be useful, (although in the case of 4 and 5 you might receive this information anyway by keeping a listening watch).
Checron - I am not so sure about assuming they will have your position - they may, or may not, depending on the service they are providing. If OCAS they are more than likely to transfer you to D and D anyway.