Firstly It was bit confusing to me to get that how to use alternate state, The purpose of this is , that it is useful when you are doing comparative analysis , If you want to show same charts having same dimensions and expression but with different selection parameter on same filter in comparison to each other.
It is almost like detaching your chart from filter or other association but also attaching it with a particular filter and association.
How to apply it ??
1. Go to Setting-->document properties-->general tab-->Alternate State--> add A and B
2. now click on your charts -->General tab--> Alternate State--> put A in it and same step of other chart put B on it.
3. now to associate these charts with filters go to ---> properties of filter---> Alternate State--> Put A and same step of Filter 2 put B on it.
4. now these filters are associated with those charts .