Subscriptions provide a management boundary for governance: they are the boundaries you assign with Azure policies. This is necessary because solution lifecycle management and authorization can vary. By using subscriptions, you can group solutions together and subscript them with appropriate security configurations.
But the Subscription Democratization design principle does more than just align subscriptions. For example, the principle also raises awareness about cost management. It is possible to group solutions based on costs. For each subscript you then have control over the costs with budgets. Because the standard Microsoft account is also grouped by subscription, complex calculations for more insight and/or charging are unnecessary. Application teams can assess their usage and take proactive action to reduce unnecessary consumption of Azure Services.