i think ( and i might be wrong ) is that you can only go down to a certain size with pinned blades and pinles you got more of a size range as for any other reason i dont know as never used pinned , years ago pinned was more popular whereas these days i think pinless machines seem to be the trend on more expensive machines
With pin bladfes you are limited what patterns you can cut.
Most designers design patters for pin-less blades now.
Look at all the Christmas ornaments you can not make with a pin blade.
It takes a big hole for inside cuttings.
FD Mike