I think it depends on what kind of story you are writing.
If the characters travel around a lot, whether it be throughout an entire world, a country, or even just a city, having a map can be very helpful to track where the characters are going and what kind of terrain would be expected. The map doesn't need to be of the entire world either, just the area the story takes place in. It also helps the readers keep track of locations and can even be used to progress the story, eg. characters have to get from A to B but looking at the map they have to pass through locations C, D and E where they will probably find trouble and adventure.
But it isn't really necessary if you don't want one. I personally love maps, especially in fantasy stories and I also love creating them. So all my stories have maps I am working on but these three were just for fun and I have no intentions of setting a story in them.