is it necessary to conduct a survey after your promotions?

Answer 1

It depends ... whilst the ideal answer is 'yes', surveys cost money and the total cost of the promotion + survey may mean that even if sales go up, you end up making a loss overall.

Say you are promoting a product via advertising .. if you see a significant increase in sales, then you can say the promotion worked !

If the promotion is by Coupon etc. then just count the coupons that have been redeemed

But if you are promoting 'brand image' or 'brand awareness', then how else are you going to judge if the promotion was a success's ?