The instrumentation has a performance overhead.
You enable the instrumentation with a prepend_before_action,
e.g.
prepend_around_action :callstacking_setup, if: -> { params[:debug] == '1' }
When the request is completed, the instrumented methods are removed (thus removing the overhead).
You have to enable it judiciously. But for a problematic request, it will give the entire team a holistic view as to what is really happening for a given request. What methods are called, their calling parameters, and return values, all are given visibility.
You no longer have to reconstruct production scenarios piecemeal via the rails console.
I'm not familiar with rails, so sorry if your reply above inherently answered this.. So you're enabling the tracing with a call in your controller method, but how is the tool capturing function params and returned values for sub-calls in the respective controller method?
Is it waiting for execution to return to the controller method and polling the stack trace from there?