Cache control value control in a static resource:

Private- It specifies static resource data cached on the Salesforce server shouldn’t be shared with other users. The static resource is only stored in cache for the current user’s session.

Public specifies that the static resource data cached on the Salesforce server be shared with other users in your organization for faster load times.

https://salesforce.stackexchange.com/questions/9038/what-does-the-cache-control-value-control-in-a-static-resource