Usually yes.
The shapes you pose yourself will match the actor’s facial expression limits.
The shapes that metahuman puts up on the character are standardized.
The metahuman animator (and livelinkface) try and adapt the morph visually with the depth perception.
Both performances are fairly similar, but the one where your poses are driven by the limits of the actor’s actual face can achieve and provide a better match for the - in between - values which are normally used during the animation.
That generally leads to a closer to real end result.
Also, some actors - take Jim Carrie for one? - Have facial poses which by far exceed the norm that is given to standardized stuff (because he just isn’t standard I guess?).
When working with people like that you either use a custom rig, or even ArKit wont be able to match up expressions…