Conditional code can stay broken for months because the active editor compiles only one platform and define set. Platform & Define Compile Matrix Guard reads the paths your project can reach, plans a bounded matrix, and compiles them with Unity's own compiler before the release branch exposes the problem.
What it helps you do
Use it when platform-only code breaks late, feature defines multiply, asmdef constraints become hard to reason about, or one CI job cannot afford the whole matrix.
The tool compiles; it does not build, link, run, or certify a player. A clean matrix proves the planned compile cells passed, not that every possible define combination or platform runtime is correct.
Read the complete documentation.