I can't say I did much w/ NT and parallel ports beyond attaching printers. I'd imagine it could be pretty awful in the "SPP" days, especially with people trying to connect ZIP drives, "Backpack" CD-ROM drives, tape drives, etc. I suspect floppy drives, which I also didn't use under NT very much, could also play hell w/ interactivity.
I think NT still had problems with interactivity when the parralel port was used (interrupts)