[zimbatm]

coz requires the user to instrument the code. So it's interesting but also much more costly to run experiments with.

I suspect it's cheaper to start with callgring to get an idea of the hot spots in the code base, find the low hanging fruits. Then switch to coz if you really need to squeeze out the last performance juice.

[vanderZwan]

If you watch the talk, he finds a number of examples of already implemented optimizations that don't work. I wouldn't be surprised if it was better to immediately start with coz. If nothing else, it forces you to model the problem better so there's overlap with test driven design there, no?