The idea "in hot code" slides try to express is very simple: if you have a JavaScript function that should run as fast as possible then don't do this and that.

The idea "in hot code" slides try to express is very simple: if you have a JavaScript function that should run as fast as possible then don't do this and that. Going into details requires a lot of speaking/writing so it was not an option for a 40m talk. I would not say that knowing which constructs should be avoided is meaningless. Of course it's great to know WHY they should be avoided but that requires deeper understanding of VM internals. Trace parameters are there to give actual nodejs/v8 users a chance to experiment, to trace their app and see what optimizing compiler does to their code.