I don’t believe it makes any material difference to delay attribution as, in years of being asked for delay reports, I’ve never once been asked whether I pressed SG.
To give the converse of that.
In years of pressing the SG button (and entering the delay reason into DAS) I don't even get asked for delay reports. I genuinely can't remember how long ago my last "please explain" was, but I'd be counting in years rather than months.
I also exercise judgment, but it's possible that my own judgment is different to others.
I would use SG immediately if being stopped would cause or exacerbate a delay, or if it appears that I've been forgotten about or the signaller is shuffling the booked order of trains without apparent cause. I don't know the extent to which signallers can and do forget trains, but my experiences suggest that just sometimes they do (even when you're stopped right outside their window). If my behaviour causes irritation to a signaller then I apologise, but I'm more than happy to get off your panel if only you'd give me the road and will be gone in a jiffy. Sometimes it really does pay to get into the signaller's eyeline.
I would also say that I don't think it's necessarily fair to assume that I know what's happening ahead nor that the reason for a delay can always be discerned by the behaviour of the signals. If something feels wrong then, again, I will SG immediately just to let the signaller know that my train is at a stand and that it's safe to call me if necessary (not all signallers use the "Call Signaller" function). After all, that is what the function is meant to be used for.