This config is not documented on purpose, but we may reconsider that. It is one we typically use only for analysis.
The Async Profiler's area that deals with recovering stack trace frames is known to be sensitive in some systems. It is used as a bit mask with values between 0 and 31, where 0 enables all recovery attempts and 31 disables all five (corresponding 1, 2, 4, 8 and 16). See comment by the async profiler author on the corresponding GitHub, explaining why 16.
No. Using 31 means disabling the recovery of stack frames that failed to be obtained in the original stack trace capture. Using 16 means disabling it when occurs during GC.
This has nothing to do with the stack trace capturing that the agent does for spans, it is only relevant for the Sampling-profiler mechanism.