>>76520608
It would feel better because you can get in deeper. Figure that you can only thrust until your hips hit her inner thighs. When she spreads that wide you are guaranteeing that you can get fully balls deep each thrust, and at a better angle.
>inb4 big dick larp
Alternatively you can also spread the legs and push them back to get the same thing. It's a different angle bit works if the girl isn't a gymnast.