Well I'll fully admit to using marks on the meter and can't see how I could be competitive without them.
My memory sucks and after awhile it becomes VERY important to remember just where 8 feet is on your putter, or 150 is on your 155 clubs etc. The top players know after 100's and 100's of rounds as most people would but for those that aren't there yet and don't have the kind of time it takes to put in those rounds, they are a much welcomed help.
I do agree that too many marks makes it just math, but a few like 2 or 3 would help and still leave plenty up too feel, not too mention wind is all feel (though I think top players have this calculated) and so is the break in each green feel (harder to have a calculation for luckily).
2 or 3 marks basically just simulate 3/4 swing, 1//2 swing, which on the real course you get good at after awhile but true, you cant just stop your swing on an exact mark like you can here if you were to have them. Really just a couple would help with judgment more than anything and most shots will be left to the "feel" element.
I know the purists out there would still want no marks and not everyone will ever agree on this subject.