Ideally yes. It is possible to grow without an EC meter, but you will have no idea how strong the nutrient solution is. This can lead to excess nutrient feed problems which will harm your plants. Measuring EC will also give you a good idea of how much your plants are eating. If you're using salt based nutrients, it would be highly recommended you use an EC meter to get the best diet to your plants. Organic nutrients are not salt based, so will not be measured on an EC meter. Because of this, if you're growing organically, an EC is unnecessary. Find out more about EC and how it works, here.