I always butt mine up as tight as I can get them.
Any slight flex is going to cause all the gear squeezed in the joint to come loose.
Fibre tape with then move causing a crack.
I could be wrong here and I'm sure someone will say if I am but I was always under the impression that square edge boards are supposed to be butted up.
Tapered edge boards are supposed to be for tape and joint and they are Tapered so you can get gear in the joint to bed the tape.
Agreed....
To me a 3mm gap in any of my board work would be where I've struggled with something or something run out etc and would double scrim that join before skimming or even back filled with gear first then bed scrim down...
I think its a massive ask for that ceiling to have not cracked without prior remedial work before skimming...
Feel for the bloke though as he's obviously tried to do what he believed to be the best job apposed to shody not caring work...
At a glance looks neat but its definetley 100% the 3mm gaps that have caused the problem IMO!