What triggers self-service sign-up for Azure Active Directory Email-verified user?

we are planning to provision all users via AD Connect server, no users will be created directly in azure AD.

upon checking Azure AD, some users already have pure cloud profile with property: Azure Active Directory Email-verified user.

What triggers self-service sign-up for Azure Active Directory Email-verified user?

is it ok to turn it off?

Set-MsolCompanySettings -AllowEmailVerifiedUsers $false -AllowAdHocSubscriptions $false

https://docs.microsoft.com/en-us/azure/active-directory/enterprise-users/directory-self-service-signup

tnx