Whenever you Enter an Activity, you will see two blue button options to save it at the bottom of the activity window:
Each does what it says: the Save button only saves the activity, whereas the Save and Exit button saves the activity and closes the activity window. Usually the right-hand Save and Exit button is most efficient. (And, as usual, the Cancel button discards your changes.)
The reason CARES also offers the standalone Save button here is to make it efficient to add an attachment to an activity as well. The only time you need to use the standalone Save button is when you want to add an attachment to a new activity.
When you first create any activity, it is only a hypothetical piece of data until you save it. CARES cannot upload an attachment to something that doesn't yet exist. Therefore, CARES offers the standalone Save button so you can save--i.e. make real--the activity and add an attachment to it in the same window (without needing to close and reopen the activity to do so). However, if you accidentally Save and Exit without uploading a necessary attachment, you can always edit the activity from the Appointment Activities Tab and add one or more attachments later. See also Attach a Document.