Does "build independent case" actually do anything, then? I've been ignoring it so far.
After doing it for a while, you will either get a success or a failure. I believe it's related to your logic skill, and I've never had a success so I can't tell you what you get, but I have failed twice and it it just a minor performance hit. It might also hit you coworker relationships, not sure.
According to the GameplayData.package file...
Build independent case actually causes your performance modifier to dip by 1. Sort of like bumping your mood from "Elated" to "Very Happy", down by 1 level.
The time taken to complete building the case is 600-1080 mins (10-18 hours).
As for success rate, it depends on your logic skill. Above level 7, it will always be successful. Below level 7, probability of success decreases linearly (not too sure what this means, ie if level 0 gives near zero chance of success).
Upon success, your work performance gets filled up by 75%! So, if you calculate the losses you're taking over 10-18 hours at a performance penalty of -1, maybe you can see if it works out profitably.
Upon failure, your relationship with every co-worker takes a hit of -5. Is the relationship scale 100? Ie, -50 to 50? Or 0 to 100? Or -100 to 100? Not sure about this.
Ok, that's all I can read for independent cases from the GameplayData.package file.
How does mood factor in? Are there any modifiers for sending a Sim to work in a great/terrible mood?
Mood is a "performance metric." See point A.
Does building skills not have any effect on stress level? I never noticed a performance decrease, but I thought it added more stress.
I assume Office Hero modifies work socializing in the same fashion that Schmoozer does.
Also, how quickly does performance decay while you are missing work? And what the heck is up with the Vacationer reward, I have no idea how that work. I have no option to call in, and if I just tell my sim not to go, I still get a performance hit for being missing. How does this thing work?
The Vacationer reward seems to reduce performance decay by a factor of 0.2. Ie, decay is reduced to one fifth of normal.
The performance flow when missing work seems severe: -10. That's even more severe than the being at work in your worst possible condition: -8.
So, with the Vacationer reward, it seems missing work will only give you a performance flow of -2.
I do hate the fact that any performance gains when performance bar is full (100) is wasted. Weird.