I picked up a ND 1000 filter that I could use on our Canon Rebel XS DSLR a couple weeks ago. You can use it to flatten out water or blur parts of your image that are moving because it allows you to take daylight long exposure. Part of the reason for the delay in trying it out was because I would need to use the Manual setting on the camera. This would require my brain. I'm going to detail the steps here so that I can reference it in a couple years when I have forgotten.
Without the ND 1000 Filter
With the ND 1000 Filter
Just to recap... I am not sure I prefer the photograph with the filter. I'll have to try out some different subjects and report back later. Click here to see that post.
Here's a time lapse that I did on the GoPro Hero 8 Black.