Quick post here...I read a lot of articles about "What should I get for my DSLR video?" and everyone seems to quickly go to follow focuses, matte boxes and shoulder rigs. Its pretty easy to just straight to the glitzy-glamorous pieces of gear and fly right over the ones that are going to actually effect your final image.
In steps the lowly ND filter. ND filters essentially just cut out light hitting the sensor without having to close down your aperture, thus eliminating your creamy shallowed depth of field. (Which is the whole point of these DSLR's) By using these filters, your images color and saturation isnt changed, but the light is simply blocked out. This can get tedious will all differnt amounts of light blocking (different amount of stops) over multiple filters, which is why the variable ND filters are so great. Its all the differnt levels of ND in one adjustable filter!
If you want to shoot in the broad daylight and have any sort of shallow depth of field, youre going to need one of those ND filters, its as simple as that.