Trade-off between await-ing a "child" boxed future vs spawning/awaiting a new task on executor

[atagunov]

https://internals.rust-lang.org/t/questioning-the-design-of-the-future-trait-and-the-cost-implied-by-it/14217 includes information which IMO should be 101 of working with async in Rust, in particular in comments 16 15 and 13

Line charts from post [16] are also educative. This thread has been extremely instructive and is most definitely worth being prominently reflected in the book