Let’s say you have three departments that use a collection of Sinch products: The marketing team uses Conversation API, your customer service team uses Voice API, and you send meeting reminders internally and externally with the SMS REST API.
To keep the activity of each department separate, keep each in their own Sinch project.
Let’s also say you sell Sinch products as an ASP through your customer service team. Perhaps under your customer service project, you might choose to create subprojects. With each subproject having its own ID, display name, and completely customizable labels (for metadata), the Subprojects API is flexible in suiting to your business needs.