What does the warning refer to? Does it mean that "synchronize all users and devices" is for production deployment only? (see the 2nd link below). And we should generally filter only for pilot deployment?
Why should we filter?
For production, if we are to filter and we only want users and groups to be synch from on premise AD to Azure AD is there an option to synch just the Users OU and security groups. Should I select the OUs: Builtinand Users. see blue circles- step 6
https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-install-custom
dsk