Though not 'pure split filtering' I sometimes make an exposure to give a flatish print and beef up the shadows with the hard filter...or take the edge off bright highlights with the soft. Whichever seems to be lacking with a straight prints using a grade that otherwise give a decent starting point. Ultimately you can do what you want, using any garde you want at any location on the print. Things to watch out for are using the soft grades too much for 'easy' burning in. eg. If you need to burn in some sky, complete with nice white clouds, using a soft grade will be faster for the burning, but may give muddy dirt looking clouds with no contrast. Using a higher grades will take longer but may give a more lively rendition. However, if you seek to only give tone to a whitewashed wall in the sun that is burned out, a soft grade makes sense as there is no texture requiring contrast. Barry thornton talks a lot about this in his 'edge of darkness book' - a good book to get your hands on!