Is it mandatory to take GST Registration in other state?

Turnover fle registration calculated on PAN basis. If turnover in one state cross threshold limit than you have to take registration also for other state. 

While calculating turnover for threshold 10L/20L/40L, we take turnover of all the states for registration. If existing and new branch put together more than threshold limit for registration, need to take registration in new state also (even if Turnover in new state is below the threshold limit) provided that new branch make taxable supplies in that state.