In addition to various issues already mentioned, there are also some build systems that do build in parallel and produce builds or build artefacts that are goin

In addition to various issues already mentioned, there are also some build systems that do build in parallel and produce builds or build artefacts that are going to depend on the order in which threads finished, which may vary from run to run. I'm not saying you cannot build in parallel and end up with a deterministic build: that is done all the time. What I'm saying in that there are cases where some care has to be taken.