The reason to spread across multiple threads is to better utilise multiple processor cores. So the idea is to end up using less CPU to do the same thing. Unfortunately, and probably largely because it's difficult to do, especially in a realtime sim, it was apparently causing some issues for some of us. Hence it's switched off by default now. Your teammates were probably fine before build 930 and should be fine again now with build 946, though the game may use a little more CPU than before because ISI have said the tyre code is now higher fidelity. But I think I'm getting the same sort of performance I was before. So because you didn't have any problems you probably won't notice any difference. When they can sort out using multiple threads without introducing bugs it will help more people cope with the processing power needed, but if your PC was coping without it you probably won't gain much by having it on. You might be able to run larger grids (AI) than without MT, but that's probably about it. One thing MT definitely won't do is affect the actual physics outcomes. So apart from CPU load, and therefore potentially how much you can throw at it, it doesn't actually affect, or change, anything.
The multithreading improvements were added to 930 but some people had problems with it and the exact cause was hard to pinpoint. So now it has been disabled by default. So basically it's back to he way it was in 910. The extra threading was there to help out with large fields. With a fast enough CPU it probably wouldn't matter one way or another. If you didn't experience problems in 930 then setting the thresh to 3 is probably fine too. It's the same physics though. I think some people are thinking the MT code brings better physics. That isn't the case though.
