I ALWAYS use the transponder. Having done all my training at EGCC, I appreciated the help that it gave to both me & ATC.
I use the listening code when using the M/cr LLR, or indeed anywhere around the M/cr zone. I've only been called occasionally, usually to advise of conflicting traffic and only once when in danger of accidentally drifting out of the corridor in poor vis.
The comfort factor works both ways, hopefully making life a bit easier for the ATC at MAN, and a 'safety net' for me. I'd sooner be 'shouted' at rather then receive a 'phone call or a letter after the flight!
When flying across hostile terrain it could be a life saver should you have a problem, always assuming that radar can still see you and that you are talking to someone. Why take chances?? It's a bit like driving without headlights on in poor visibility....