When I took on photography, there were a lot of filters to consider. ND, Haze, warming, cooling, grad-ND, polarizers. Heck, I had so many filters that sometimes they needed a little bag of their own inside my photography bag. Today though, most of the filters can be mimicked with photoshop.
Landscape photographer Mark Denney makes an interesting point, he shows three of the more common filters, ND, Grad-ND and a circular polarizer and while two of those filters can be replaced with photoshop-work. Mark asks a simple question, would you rather be spending your time editing in front on a computer, or hiking and shooting behind a camera.