I see bikers using hazards while filtering. I think it's a bit pointless cos if Mr/Mrs car driver hasn't seen you already then the hazard lights aren't going to do any good.
I had them on my FJR1300 and I think I used them once. I didn't use them on my V-Strom and after a year of owning the Fazer I only switched them on to see if they worked.
There are situations where using hazard lights can cause confusion but to be honest most people use them in all the wrong situations, the cops aren't going to do you for it. At most I think you would get a slap on the wrist - you're more likely to get a parking ticket for parking on double yellows with your hazards on because you're on double yellows, not because your hazards are on.
As for HGV drivers... A couple of flashes of the hazards or a right,left,right,left is good. One single flash seems a bit impolite. Also when flashing HGV's in, make sure it's a good long flash or preferably a short flash followed by a longer flash - too many drivers now give such a short flash you don't see it, they seem to be afraid of doing it properly.