SaaS mode now allows you to restrict the number of contacts that can be created in a sub-accounts.
The contact limit is NOT A HARD LIMIT, i.e. more contacts can still be created in the sub-account even after the limit has been exhausted. Just that an un-dismissible warning message (as shown below) will be shown on the contacts page asking the sub-account users to upgrade.
TABLE OF CONTENTS
Configuring contact limits for SaaS plans
The contact limit that is set on the 'Manage Client' page overrides the limit of the subscribed plan for that sub-account. If the sub-account upgrades their plan, then the limit will also be reset according to their new plan.