The Salesforce Sandbox integration is a feature that allows you to test before integrating Salesforce fully. If you aren't familiar with sandbox environments, especially Salesforce sandbox environments it may not be something you need to set up. It isn't required in any way.
When you are using the Salesforce Sandbox it is important to know a few things.
You can't have the sandbox and the standard integration connected at the same time. If you start with the sandbox you will need to fully remove the integration before the full Salesforce integration can begin.
Stay aware of your Salesforce API limits - very large integration tests can max out limits depending on your account.
Sandbox accounts have something called a “refresh interval”. Every time this interval passes, Salesforce refreshes the sandbox to the current state of the production environment. This means our access is also revoked, al the user must integrate the sandbox again. Check out the refresh intervals here.
If you create the sandbox integration soon after a refresh, then the sync should complete and allow for usable data. However, depending on the size of the integration this may reset before everything is completed.
The accounts/leads in SFDC will not connect to the accounts/leads in Leadfeeder - this is due to the sandbox being a test only environment and protects your Salesforce data from being updated.
The removal of a sandbox integration can take, on average, up to 24 hours, if you try to reconnect the sandbox or integrate with the full Salesforce integration before the removal is complete it will fail.