Once you get your jossa counselling seat then again if you go for csab then your josaa seat will be taken and you will be given the special rounds seat. So if you have already got a good college in josaa counseling then do not go for csab counseling. It's not required 

Hello Aspirant
If any student already get college in josaa counseling then after if they also got seat in csab counseling then after you have to decide that which is important for you , which one is good . If you will not be getting better colleges then josaa then you have option either you can accept it or you cancel . It is not necessary to take.
Thanks