It can be hard to walk while wearing a diaper if the diaper is a thick diaper or it is really wet.
However if wearing a thinner diaper and it's not wet then it's basically the same as walking in underwear or boxers.
But as the diaper swells up some from being wet the diaper expands and gets a bit bigger between your legs and so if it's a good absorbent diaper then it can spread your legs apart.
But thinner diapers don't tend to spread your legs apart much and so it's easy to walk in those.
However if you get a thicker adult diaper then you can feel the bulk between your legs and you can feel your butt and thighs rubbing against the diaper which can feel awesome.
If I begin to wet a thick diaper I can start to waddle some but it's not too hard to walk in them once you get used to it.
Even toddlers who wear disposable diapers tend to have a hard time walking in them as they get wet.
I've noticed toddlers wearing disposable diapers would waddle some as the diaper gets wet and you can see the diaper bulge in their pants as well.
However when the diaper is dry they don't waddle as much.