So, my game Sector 12, would have greatly benefited from this.
I have many instances where I needed to compare the total power output (a variable) to a large number of numerous input variables (smaller sub-systems that drew power) and I ended up having to make an event that just had like a billion nested conditional branches specifically because this feature did not exist. These different sub-systems and the power output itself would go into different states depending if power input was higher, lower, or at threshold, so it was a huge pain in the ass to event, and would have been much simpler had this been around.
I don't really understand the mentality though that such a feature needs justification to be approved. If it helps even a portion of the customer base and it is something many people would like to have, why not do it without making people jump through hoops to justify it? Just make the customers happy.
Edit: I took a bunch of screenshots of some of the code from just one event from Sector 12:
Being able to break this down into separate events/event pages with the control variables being input right there would have made this whole process much easier for me and it would have been waaaay less messy. Granted, I was ultimately able to make it all work by just making a billion conditional branches in the event editor...but it is ugly, difficult to debug, and just overall a huge pain in the ass, not to mention its potential for lag.