This piece of advice is also valid in languages without GC. In C++ it's well known one should avoid allocating memory in tight loops, and it's strongly advised to call e.g. `reserve` on vectors to avoid allocating.
free() as well as malloc() and related have significantly complex algorithms behind them, unless one can simplify base memory management in certain ways - and those ways tend to also allow region-enabled GC to outperform them anyway.
[1] Allocating memory in many Garbage Collected systems can be down to one instruction, and if using per-thread heap, it can be atomic add without CAS