Nobody cares about the number of stack frames because JIT optimizes it on its own

More other, inlining things may break some JIT optimizations and slow down the execution

inline

in Kotlin allows: 1) to skip creating objects when using lambdas 2) to reduce method count for trivial methods 3) to get richer control flow

A more complete advice is to respect IJ when it tells you that something shouldn't be inlined

Actually I am surprised it is NOT in the docs https://kotlinlang.org/docs/reference/inline-functions.html