Its bizarre actually who does use the Captain ****e.
BALPA do until you tell them not to.
If you have interactions with some Mil units the letters etc are addressed to Capt. but I can understand this with rank structure etc.
I don't mind work stuff to be honest going to the company but if its sent too my home address I get a bit annoyed especially when they just presume even after filling a form with Mr on it. Once ordered some 4 bars from an online shop because I lost mine and they got delivered to Capt MJ.
There are some knob Jockeys out there that use it on every bit of paper work they can get it on. I have no doubt There are cards/paperwork out there with Capt Robert Weaver on them.
I haven't a clue who should use it and who shouldn't, Some areas of the world every pilot is called Captain. The only time I get called Captain in Europe is when very rarely when I have had to have words with handling or ground crew or the ramp rats are taking the piss.