The following are best practices for both tenants and subscriptions:

• Keep subscriptions to a minimum to reduce complexity
• Segment bills by leveraging tagging, instead of creating more subscriptions
• Use resource groups as application lifecycle container boundaries
• Use RBAC to grant access and to delegate administration

However, you should avoid these practices:

• Do not create a subscription for each of the development, testing, and production environments to protect quota and enforce security. Instead, leverage the features of Azure DevTest labs (an IaaS solution), App Service Slots, or opt for Azure DevTest access using an MSDN subscription (as this creates an issue with cross-subscription sharing, like wildcard App Service Certificates which are stored in Azure KeyVaults and other subscriptions can't share them).
• Do not consider enforcing quota is necessary—use Azure Resource Manager (ARM) policies to help manage quotas.
• Do not create multiple subscriptions just because you need to have separate bills for each department—tagging can be used to separate out the costs instead. Separate subscriptions introduce the need for a second layer of networking infrastructure, or for cross-subscription virtual networks through site-to-site VPNs. While it is possible to do, it does increase complexity.
• Do not use a subscription as the primary method of delegating administration. Subscriptions should be a very high-level administrative container, but that’s it. However, it might make sense, for example, to have one subscription per IT department in a company with multiple IT departments.
• Avoid spanning applications across multiple subscriptions, even with multiple environments, because it reduces your ability to view and manage all the related items from one place and on one bill.
• If you have multiple subscriptions (for example, Azure DevTest access on an MSDN subscription), don’t split these subscriptions by development, testing, and production; instead, split by groups of apps, with each entire app and its related apps contained within a single subscription.
• Do not proactively split subscriptions based on the fact that, eventually, you will need more resources. Resource limits are always increasing, so by the time you may get close to a present-day limit, it will likely have been increased.