It’s easier to track what quests your friend is on and where you need to carry them on 2 seater. You can also actualy play with your friend that is far behind you in progress and they can also actualy play with you.
It’s personal but getting carried by someone who just one shots everything you need to figth with is just plain boring because you don’t have to do anything. When you activate party sync you can actualy play and have fun together and overcoming “challnges” together. I find it more fun that just carring someone or being carried.
But with P-Sync the higher leveled friend also gets a rewards aprotiate to their level, instead of just wasting time trying to help a low level friend that will quit two weeks later by driving him in your two seater.
Sometimes getting carried is extremely boring.
If your friend is, unlikely but hey, new to wow or mmos in general, playing with them on their level is much better experience for them than afk while you one shot their mobs, and has a bigger chance of getting them to keep playing the game.
I think it could well be a gateway feature to a forced mode further down the line (personal loot in random instance, then in all regardless as an example).
I like doing new content and pulling my own to work towards stuff on my own or part of a team. But levelling up, for me personally is boring as hell.
Spent many years levelling many characters on US side, I struggled to bring myself to do it again here. Then they nerfed the xp gain and xp bonus etc, which put me off all together.
So yeah I think it will be a feature you can enable and disable at first, but I would not be at all suprised if this led to it being forced for everyone in the future, just to kill off any kind of effective carrying.