By syncing data to a particular field in Salesforce, you're effectively saying that the source of truth for that field is the warehouse, and not Salesforce. If you expect a human to update a field, then Salesforce is the source of truth for that field, and Hightouch shouldn't write to it!

What we typically see is that Salesforce contains data that's expected to be updated and maintained in the tool, and then other "read-only" fields coming from Hightouch.