you are redirecting to another model when doing such operations. So id must be related to the current model record and the parent will be active id. This is useful to filter out the related records or doing extra operations with the parent records.

for example Employee -> time offs

you can access time offs from the employee profile, while doing so, the employee is parent record and time off as child. while clicking the smart button you will be redirected to the time offs model. hence the id must be the time offs and active id should be employee id.