Snapshot Reports are intended to be used as a prospecting tool and as such are typically expected to only be generated once during the prospecting phase.
Creating a Snapshot Report and refreshing a Snapshot Report are two separate products and both charge a standard fee of $2, however, some subscription tiers have a number of 'free' Snapshot Reports allocated which can only be used towards creating a new Snapshot Report for prospecting purposes.
Although a Partner can refresh a Snapshot Report, this will incur the $2 charge as this is treated as a separate product from creating a Snapshot Report.