if you need to boot some program it's easiest to do it from the floppy.
But the floppy drive (at least all of them) won't plug into the same slot as the other optical drives/ata hdds. Don't know where you got that most new mobos don't support more than 2 pata devices, but at least I have never had problems having a dvd drive & hdd on the ata slot and the the floppy on it's own slot.