A child should wear diapers or training pants while potty training so as to prevent them from getting their pants, furniture, floor etc wet or poopy.
Some parents potty train their kids with underwear and that's okay as well but there will be urine and poop accidents on furniture, the floor etc.
Having the potty training child wear pull ups or a diaper until they can stay dry is much more sanitary and keeps the house clean as well.
Diapers can be used while potty training as long as you remind the child that they are wearing the diaper just in case and they still need to use the toilet and not the diaper.
Don't punish the child if they use the diaper instead of the toilet.
The child is so used to being able to potty in the diaper that it takes time for the child to get used to using the toilet instead.
Yes training pants and pull ups are less absorbent than diapers are.
Although training pants and pull ups are really just diapers that pull on and off instead of being taped on they are not mean to absorb large amounts of pee like regular diapers are.
With regular disposable diapers they are meant to absorb lots of urine from a baby or kid that is not potty trained because the diaper is the kids or babies potty.
But training pants or pull ups are meant to just catch urine if the child does not make it to the toilet.
Pull ups or other training pants also leak more than regular diapers do.
I find that keeping the child in diapers while potty training is much better.
Regular disposable diapers are much cheaper and more absorbent than pull ups or other training pants and you can remove the diaper when the child needs to use the toilet.
Also teach the child to remove the diaper and put it back on such as sliding it on and off and then tighten the tapes.
Training pants which are also known as Pull Ups which is a brand name are just pull up type diapers.
The Pull Ups or training pants are not as absorbent as regular baby diapers are such as Pampers, Huggies, Gentle Steps or other diapers but they do catch some pee if the child does not make it to the toilet in time.
However during potty training it's best to just keep the child in a regular disposable diaper and remind them to use the toilet.
Take the child to the toilet when you think the child is needing to use the toilet to pee or poop and remove the diaper and then put the diaper back on the child if it's clean.
Remind the child that they are wearing the diaper just in case but they should go to the toilet when needed.
Eventually once the child can keep the diaper dry or at least partly dry for a few hours in the day then they can go to wearing regular underwear.
Or you can just put the child in underwear and then deal with the pee and poop messes that happens.