Guide explains how to use bath at camp for boost morale.
Guide to Bath
So you boost morale of general centurions / pretorians. And change the moral status.
Another thing is that the bath can boost the Legion morale wich is very useful in act I but for that you need a Praetorian with the social perk. Unlike the praetorians that just stop be assigned in the bath when they recovered the approval to the limit allowed by the tier of the bath the one with the social perk can be here indefinitly since he restore the Legion Morale at the same time and that perk is still useful for ACT II because of a certain reason
But its not works like: keep one up and the rest will benefit.
You need to post one at the time for those you want to raise the approval the social perk is for the Legion Morale only as i know as for centurion i don’t know if the social perk work on them for the Legion Morale.
So just put a centurion with the social perk in there and leave him in there. 4 extra morale each day or so really adds up.
The bath is for improving the mood of praetorians. The problem is, that they can only be put there, if the mood is really really bad. You can get upgrades, but even on the highest upgrade, you can improve it to somewhere in the middle.
The only real benefit for them is, if you put some guy with social skills there (as jonandbeth wrote). This way you get some moral bonus for your legion.
If you put a low satisfaction legionary there, they will recover morale up to specific level (e.g. first level bath will only raise moral to “Apalled”, never higher.
Additionally, instead of low satisfaction one, you can put a legionary with “Social” trait. This way he will give a morale boost to your legion every 36 hours.