Do we need an OWA Server

Do we need an OWA server to preview documents?

No – You do not need any OWA Server – Preview is 100% independent
Preview does not in any way use or require Office Web Apps servers and is not influenced by the performance bottlenecks imposed by this architecture.

The preview file is pre-generated by the Preview conversion server(s) and loaded instantly or on demand. Scaling is possible by installing multiple conversion servers.