When potty training a child it's not required to use Pull Ups or training pants when potty training.
But potty training a child will result in a mess if you do not use Pull Ups or training pants on your child during the potty training.
Without Pull Ups or training pants the child will have wet underwear and possibly poop filled underwear if they can't make it to the toilet.
So using Pull Ups can help as it keeps the poop contained and absorbs the pee should the child wet their pants instead of making it to the toilet.
I would highly recommend using Pull Ups or other potty training pants when potty training because they really do help and the child can pull the Pull Ups up and down on their own but they're there just in case.