The non-committal grunt is neither a refusal nor agreement; rather, it prompts continuation of the conversation without exposing your position. It can also be used in lieu of the Yup, especially those cases where you want to avoid inadvertent agreement.
Can be employed as a more politically correct version of whatever or pfft.
When deploying the non-committal grunt, one must understand that they are stating the following:
“I hear you and acknowledge that you have stated your position and are expecting a reply before continuing; however, at this juncture I am not committing to subscribing to your point of view.”
“You are the man!”