Why we go for Batch Reactors?

Batch reactors are basically used for chemical processes that are time or reaction bound. In other word if you are producing product C that requires mixing compounds A & B in the presence of heat, and the reaction will take two hours to arrive at your desired product C, you would need a batch reactor that will take predetermined volumes of  compounds A  & B in the presence of heat and maybe a catalyst if need be.

for reactions that are immediate where you have say compounds  X + Y giving you product Z,  you will need a continuous reactor with steady feed In-flow streams and  a steady product output .