So far I have seen that because of the raised contrast/dmax, the midtones tend to have more of the color of the process revealed. For example, that Palladium print has a nice copper brown to it and the cyanotypes we have done are a beautiful blue...not nearly as washed out.
Another thought is that we've found it to be a 'paper saver' because it creates a fine layer on top of the paper, it can be used on papers that normally aren't good for that particular process. I forget the name of the paper, but one in particular was horrid for PT/PD printing, add some silica, and viola! it prints fine.
The last benefit, and I know I am beginning to sound like a salesman here, is that it takes away gloss from certain processes. We were really getting tired of the gloss on the coated papers used for Albumen when Dick added silica to give it a matte finish. Not only did it work, but then we noticed the DMAX increase. Go figure.