One consideration has to do with whether or not you are cutting unprocessed photographic paper; the rotary cutters are everything they are cracked up to be, but you do have to slip the paper under the hold-down bar (at least on the Rotatrim that I have) and this may lead to scratching of some films or papers, particularly if some grit gets in there.
On the other hand, the (cheap) guillotine that resides in the darkroom for making test strips and the like is always generating a new pile of fine iron dust where the fixed and moving blades rub at the start of the cut, so I am constantly having to clean it up.
I have a couple of old Nikor rotary cutters that are perfect for cutting coated paper. The guillotine cutters tend to pull the sheet where as the rotary is more precise. I got them used many years ago and I think comparable new ones are fairly expensive.
I cut the tip of the index finger on my left hand off while cutting paper in the darkroom with a guillotine knife. I was in sixth grade. I still have a very nice triangular piece of finger missing. Funny thing is, I never felt it. Didn't even realize there was anything wrong until I noticed the blood all over the paper and the floor.
Besides, as has been mentioned, the standard office type guillotine knife never cuts square.
I went through this dilemna years ago and finally decided on an IDEAL precision safety guillotine.
It was expensive but has now operated flawlessly for two decades with the original blade. It cuts film and paper with dead square corners with a razor sharp blade in pitch blackness with perfect safety. The spacer bar and automatic hold down clamp prevent work moving around so cuts accurate to 1/1000 of an inch are repeatable. 8 ply mount board cuts like butter.
Photography, the word itself, invented and defined by its author Sir John.F.W.Herschel, 14 March 1839 at the Royal Society, Somerset House, London. Quote "...Photography or the application of the Chemical rays of light to the purpose of pictorial representation,..". unquote.