It also builds code repeatably & hermetically (interpreted languages excepted; at google python is built super hermetically where a python binary + environment

It also builds code repeatably & hermetically (interpreted languages excepted; at google python is built super hermetically where a python binary + environment is bundled with python script(s) into an executable; some companies like dropbox have copied this). You run build, and you get binaries for N kinds of systems (e.g x86_64, ARM). It builds a dependency graph of your code that you can query and results in cache-able builds (only rebuild the part you need). Since building dependencies in a tree can be massively parallelized, it also allows you to parallelize your builds well across machines (with some effort). You use the one tool to compile C++, Java, Python, Go, Rust, etc.