Compass is useful for enabling private Tangles for anyone wanting to look at the IOTA protocol.
Security researchers could use Compass to create a private Tangle to conduct security testing and research. This enables them a controlled environment to test assumptions and produce attacks.
Developers could use Compass to create a private Tangle to develop applications in environment with unlimited tokens to manipulate.
Corporates could use Compass to develop a Proof of Concept application without sharing their technology. It allows them to test and debug in private until they are ready to launch their application on the permissionless IOTA Mainnet.