Comfortable bicycle seats are necessary if you go for a long ride. If you just ride to the supermarket to get some bread the type of seat will not matter much as the distance is too short to effect you in any way.
The type of seat is dependent on your average riding speed. If you often ride fast or tend towards racing you should get a narrow seat to avoid that the seat interferes when you pedal very fast. In this case your body weight is located more on your hands and feet and not on your seat so you don't need a wide seat.
But when you are a slow and casual bike rider who takes it easy most of the time then get a wide seat that is well padded and very comfortable as your body weight is placed directly on the seat.
Keep in mind that there are seat versions for men and women. Usually the women's seats are a bit shorter and wider compared to men's seats.