Please see the following discussions on the benefits of reproducible builds:
Not on their own, no. But the intent is to eventually use diverse double-compilation,
which can be used to detect the presence of malicious compilers or build environments.
Reproducible builds — specifically the ability for other people, not just Fedora, to build packages — is a necessary first step towards that.
Bruce Schneier’s commentary on the DDC paper explains things clearly.
Note that it requires being able to check that the resulting binaries are identical.
Without the ability to reproducibly build software with a single compiler, you can’t even start comparing its output with other compilers.