What's the use of ReActor 🌌 Masking Helper ?

[pandayummy]

The workflow seems to work without this node ReActor 🌌 Masking Helper

[Gourieff]

Without the Masking helper node the swapped and restored face appears inside the box area, but with Masking helper it appears inside the mask of the face
In this case such details as hairs, glasses etc won't be touched by the inswapper model and face restoration models

[LecterXIV]

What node should I connect on the IMAGE INPUT of the ReActor Masking helper?

[Buumcode]

What node should I connect on the IMAGE INPUT of the ReActor Masking helper?

You should connect 'IMAGE' output from Load Image node or 'IMAGE' output from Fast Face Swap node.
You can take a look in that workflow - https://drive.google.com/file/d/19BLLdVrKuavA_rchEAEDLh3ZNOAZjG7V/view?usp=sharing
Workflow make: generating image > face swap on image > correction by using ReActor Masking Helper.
Workflow grabbed from description of this youtube video - https://www.youtube.com/watch?v=d6rhJc_l5gs