Never heard of turning the transponder to STBY while close to the field and I been flying for a while. I have seen pilots switch to STBY prior to code changes.....not sure what that was all about.
Prior to the latest "ON" for ground ops change, the AIM said turn the transponder to "ON" as late at practicable before commencing the takeoff roll and switch to OFF or STANDBY as soon as practicable after the landing roll. Was that way for 30+ yrs. Transponder "ON" for surface ops has been pretty common for a while now at airports with ASDE-X and it's been the recommendation for all airports for over a yr now.