TL;DR: This is a Rust crate that enables you to log text in Rust hundreds of times faster than traditional text logging while avoiding the need for parsing to recover values from your text log. This is not a new idea, but since we couldn't find anything similar in the Rust ecosystem, we built one for everyone, including simple Python bindings for data processing.
So, it is pretty common in your codebase to need to add some “debug” log or text log. Usually you need to do that to keep track of something, debug or simply understand what was the behavior of your codebase after the fact.
So, now your robot, on its critical path is using compute cycles and memory bandwidth just for concatenating strings for the pleasure of an hypothetical human that might read it someday.
A lesson we learned the hard way at Copper: if something is done in real time by the robot that is not immediately useful for the robot, it should never have been done in the first place!