Maybe it was another variation on Vader's methods of motivating the troops.
He strangles Ozzel and Needa to death in full view of the bridge crew (after promoting Piett for pointing out Ozzel cutting corners) and then when they lose the Falcon he brings bounty hunters onto the bridge too.
He's saying to them "You guys better get your act together because nobody here is irreplaceable, if these goons can do better than you, what I use are you to me?" that sort of thing.
This is why I suggested having Piett finally having enough of this tactic in a reworked ROTJ.
It reminds me of how Caligula acts in I Claudius, (he gives high ranking generals he doesn't like amusing and humiliating watchwords to say like "Give us a Kiss" and "Bottoms up" and repeatedly kills people for seemingly bizarre reasons to keep the survivors on their toes, eventually they have enough and assassinate him).