Just a little insight from Air Taffic here.
If you are operating on an airfield that employs ground movement radar. Transponder use can be required, in which case the radar picks you up and identifies you on the blip on the airfield layout they have. Used at places where low vis often occurs, or large airfields to prevent collision and to increase efficency.
In terms of airfields not employing surface movement radar, the radar room doesn't get interference from your transponder being active whilst on the ground, as SSR radar supresses transponder codes on the ground, or airfields would just be a haze of transponder codes.