Main Engineering gets you an engineer, who applies their engineering bonus to the ship. Which is likely to be better than your ship commander, since engineers are assigned for having the best available engineering bonus (among qualified officers at the time of assignment).
Yes, I understand that. I mean, why would I care about an engineering bonus? Does it reduce the ship’s MSP consumption more than 150 tons of Engineering Spaces can? Or, do I misread the bonus effect entirely?
Whether Main Engineering is a good idea depends on several factors, such as ship size, cost, deployment time, etc. but in some cases it is definitely worth it. See the rules post below.
Thank you @AuroraSteve and @skoormit, I guess 25 kton cruiser designed for long(ish) independent voyages earned its ME.