When the Auto Populate option is on for a shoot day or period, anybody who completes an onboarding form is automatically added to that shoot day or period. This is useful at the start of production when you are setting up your shoot days and don't want to manually add each person as they onboard.
For shoot days we recommend you set Auto Populate to on, until everyone on your shoot is onboarded.
For periods we recommend you set Auto Populate to off.