Mm. Reproducible builds have a really wide variety technical advantages, including implicitly removing non-deterministic or unsafe behaviour (such as downloadin

Mm. Reproducible builds have a really wide variety technical advantages, including implicitly removing non-deterministic or unsafe behaviour (such as downloading third-party code from the internet), detecting corrupted build environments, reducing time-to-detection of a build host compromise, validating cross-built packages, the potential space/time savings you mention as well as numerous other debugging and testing advantages. In other words, even if you are an attacker, you want reproducible builds. :)