You may go further while being a soul.

However you won't be able to gain souls (purple thing in the right bottom corner), XP, any ressources, and you will spend a certain amount of souls per second, which end up extremely expensive if you don't have a whole lot of them and are strong enough already.

You can still die and that would be the final end, tho.

I would recommend using it only if you are sure you can beat a boss you were on, or to kill the final boss if you think can do it / finish it too

Otherwise, unless you are strong enough to finish it all and don't mind spending countless souls (what is used for the Soul Lantern, "talent trees" too, or trying a second chance in a game to redraw skills / cultivation techniques, etc...), then you may go for it

Benefit is only in going a bit further or finishing your game if you can