I used to depend on it heavily
@RobRenfro - I learned it before ever trying MQ so it was my "safety net" as I was comfortable with it.
big things I depended on it for:
1) seeing other toons - it was easy to have a button that cycled through the group one toon at a time swapping them to main, plus I could always see the non main in a "smaller" picture in picture type window or on second monitor
2) key mapping - ie if I press ALT+1 it will send a mapped keystroke to the other accounts, but it doesn't have to be ALT+1 on the other key binds.
3) key broadcasting (this is similar to MQs Mimic button, but MQ is a bit more intelligent about how it does it whereas ISB is broadcasting exactly the input it receives to all accounts / instances.
You can also check our discord chat and others here from me, I've talked about it a few times on the forums with other users trying to ease my concerns to drop ISB as it was consuming a ton of cycles on my PC and I wasn't able to load more than 6 concurrent accounts.
Moving away from it was my best move yet - I've quickly found the items here on RG to fill any gaps I was worried about; ie BoxHud to "see" what all toons doing or configured as (are they targeting the right person, what spell are they casting, is their combat assist set to Pause or Active, is their BurnAllNamed on or off, etc; ButtonMaster to make a standard button set for all toons for specific activities (ie doesn't matter who I hit pause from, they all do the same thing when I hit that BTN Master button).
My 2cents - if you're not doing it already, and you're leveraging MQ - DON'T add ISB. No shade to anyone who uses and loves ISB, I was that guy - just found ways to get the same old PC to run 24plus accounts and other things I wanted from it by reducing FPS and resource consumption. Maybe I could have gotten ISB to do something similar, but it was far less complex for me to just drop it and get comfortable with some of the
Lua options here on RG. Plus it has cost, always nice to eliminate that when unnecessary