Car cabin heater

Just want to know your opinions cause I don't have any ideas about cars. I just bought a used car with engine heater only. I am just wondering if it is really necessary to install a cabin heater? Or is the engine block heater enough during winter? Btw, I am living here in northern ostrobothnia. There is also a note in our parking lot that it is not allow to use cabin heater while using engine heater. Thanks in advance.