The sandbox account is used for development builds while the production account is used for ad-hoc or distribution builds. The sandbox account has additional testing tools active as well, such as a live event tracker, which can be found on the Recent page.
Our SDK will automatically detect the build type and direct traffic to the appropriate account. For iOS, our SDK will send traffic from builds provisioned for the Development APS environment to the sandbox account and traffic from builds provisioned for the Production APS environment to the production account. For Android, all traffic from builds signed with the debug keystone will go to the sandbox and all other traffic will go to the production account.