Tiki Suite should cover what 80% of the people use 80% of the time for a typical small or medium organization. The idea is to offer a well integrated set of tools for what most people need most of the time.

Free and open source software

All the regular benefits of Free and open source software (No license fee, no fee per seat, etc.)

Interoperability

Every one says they are interoperable. But sometimes, even with two pieces software from the same vendor, there are issues. It's just a difficult problem. By reducing the number of possible interactions between the various components, we'll keep the complexity as low as possible.

Community

Even if each piece of software works well, you very well could still have issues because "they don't talk to each other". A community which shares the same software interactions/combinations is in a better position to add missing features and make them stable and efficient. We'll have more eyeballs

Efficiency

By using less different software packages, this reduces training needs and increases efficiency.

Flexibility

Tiki Suite covers the most common needs. If you have specific software (commercial or otherwise) you need, nothing prevents you from using it.