If the projects are unrelated it's a good strategy. Whatever you chose, the most important challenge is to understand the implications, mainly:
With Team Project Collections you get:
- Physical and logical isolation: each collection stored in a different database. This allows maintaining each collection without affecting the others collections. Physical isolation is best for consultancy\outsourcing development scenarios.
- Better scalability.
- Each collection will require its own servers and hardware (build controller, test controller, SharePoint portals, etc.)
- No sharing of code and work items between collections.
With single Team Project Collection:
- Simpler data model, means simpler maintainability, less storage requirements and easier backups. Upgrades will be easier as well.
- No physical isolation means some users may see other projects data. However providing support should be easier as the admin team will have follow only one set of rules.
- Less system and hardware requirements.
- Allows sharing code and work items.
Bottom line, for increased security and isolation scenarios, choose the multiple Team Project Collections option. Otherwise stick with the simplicity of a single collection.