I’ve found long exposures soothing. Combined with (mostly) horizontal landscape compositions, the aim is to suggest to the viewer a sense of serenity, not unlike what Monet did so masterfully in his paintings.
Long exposure also helps free the photographer from the constraints of time: golden hour photography, though magnificent, is often difficult especially when you’re travelling. Long exposure can be used at any time of day, and teaches us that slowing down the world can be equally magnificent.
The softness of long exposure, especially when shooting water and sky, can make for some breathtaking images. There is a world around us beyond what our eyes can see, and the camera comes into its element here. It teaches us to see familiar things anew.
I also really love what long exposure on wide lenses does to perspective: there is no selective focus. Everything flattens almost to one plane, but yet remains distinct. All parts of composition are critical. What we shoot is daily new, and old.
On a personal note, long exposure taught me the value of time. Ironic, perhaps, but when you’re set up and waiting for a 6 minute or even a 2 minute exposure, time slows down; you feel every second.
My go to ND would be the 16 stop Firecrest filter by Formatt Hitech, and if I need a lighter ND I generally use the 10 Stop ND by Lee Filters and stack additional filters in between to archive the desired shutter speed, using the bulb mode.