Rigs, performace, optimize game object, expose extra transforms. Questions, questions, questions...

I've briefly looked through the forums and google but I'm still not 100% clear on a few things. So I understand that enabling Optimize game objects removes all the transform components / gameobjects from the hierarchy. And this is better for performance due to internal stuff blah blah... How much better performance wise is my first question? Is it going to cause serious lag if I don't optimise? Then theres the expose extra transforms. So this is obviously used when you need to know the joint positions etc (which I do). So does exposing them through this make for better performance? Or is it the same as having optimise off, but you can just pick and choose what bones/joints to expose therefore increasing performance in the sense of having not as many gameobjects?