Final answer:
Not enabling Chatter in Salesforce will lead to failure in the Approval Process as it relies on Chatter for posting automatic updates and notifying users about approvals.
Step-by-step explanation:
If you do not enable Chatter on the Salesforce platform, the option that will happen is C) Approval Process will fail. Chatter is a Salesforce real-time collaboration application that allows users to work together, talk, and share information. It is designed to integrate with various features within Salesforce, including but not limited to the approval processes. When Chatter is turned off or not enabled, users might face disruption in workflows that are designed to utilize Chatter for notifications or approvals. Having Chatter disabled means that the automatic posting of approval requests to Chatter feeds won't occur, which can result in users not receiving prompt notifications about pending approvals, and as a consequence, the approval processes could be interrupted or fail.
Other options like A) Document Manager not appearing or D) Documents not saving are unrelated to the Chatter functionality. As for B) Audit Placeholders, there is no standard Salesforce functionality known by this name directly linked to Chatter functionality. Therefore, it wouldn't be an effect of not enabling Chatter.
It's important to ensure that Chatter is enabled if your organization's workflows and processes depend on its features. Failing to do so can prevent users from conducting their duties efficiently and disrupt business processes that rely on the collaboration and automation features provided by Chatter.