Several years ago I had a discussion with a person that asked me pointedly why I wanted greens mower cutting heads with roller brush attachments when so many other golf courses didn't specify them with their new mower orders. Yes, they're a "pricey" option but the pictures speak for themselves.
With roller brush attachment.
Without roller brushes!
As clippings "stick" to the roller it expands swelling it and making it larger. As the roller expands the bedknive (actual cutting surface) is lifted higher off the turf raising the effective height of cut. A quick check with a height of cut gauge confirmed a difference of .010" to .030" with debris on the roller vs. a clean. With that said, if you are trying to maintain 1/8th of an inch cutting height on greens, adding .030" to you roller is giving you 5/32nds of an inch height of cut. That's was a "low" height of cut for a green back in the 70's! Now I hope you can see why I specified them on our fairway units too. Just my two cents. _MK