[lxgr]

Do reproducible builds even matter if you're building/linking and executing a binary on the same system?

The biggest benefit seems to be in making it infeasible/dangerous for a malicious actor to distribute binary versions containing different behavior from the published source.

On a local machine, when and with what would you compare your binaries?

[ShredKazoo]

Sure, just think of it as a way to get the same benefit on a precompiled system like Ubuntu I guess.