Immutability/determinism is a godsend for fast builds, because it means that a ton of of operations can be skipped - You can consult the action graph for inputs

Immutability/determinism is a godsend for fast builds, because it means that a ton of of operations can be skipped - You can consult the action graph for inputs and outputs, see that there's already a computed output matching the inputs, and skip running a compile action. Bazel is an amazing piece of software, though it's had it's ups and downs; engineered directly for Google's Google3 Codebase, without any consideration for how external code evolved - often in many forms. I tried multiple times before Python was in a usable state for devs used to virtualenvs to work with, and that was at least two rewrites by the team maintaining that tooling.