Actually, with regards to the transponder, I think the general rule is:
Transponder OFF/STDBY during startup, taxi, runup.
Transponder ALT (mode A+C) when entering the active runway for take-off,
Transponder OFF/STDBY when vacating the active runway after landing.
This is what I was taught, and what's in our checklists. I fly from a fairly large controlled airport and I have had no complaints yet.
The grand exception to this is major international airports with ground radar, who want to see mode A exclusively (no mode C, so select "ON" on the transponder) while you are taxiing or being pushed back.
Furthermore, for various reasons (usually related to TCAS alerts or clutter on controllers screens of nearby airports), individual airports or airspaces can make their own exceptions, for instance requiring that no transponders are to be used within an ATZ. But I don't think it's a general rule that transponders have to be off in any ATZ.
For the curious, read up on what the Dutch did in the SRZ Schiphol.
The difference between the OFF and the STDBY setting on modern transponders is virtually nil. The only thing I can think of is that you are able to set a squawk when it's in STDBY and not when it's fully OFF. But the earlier generation of transponders you put in STDBY once you had stable power, so that they could heat up the radio tubes or whatever, without transmitting a signal.