The general reasoning behind the recommendation is that every TCAS unit has to talk to every other TCAS unit in range, whether or not you see them on your traffic display. At busy airports or under busy airspace, the rate at which TCAS units can update their situation is reduced by having many other units to interrogate.
You don't need TCAS on the ground, so turn off TCAS (but leave on the relevant mode C/S squawk for Advanced Surface Movement Radar) until ready to get airborne, or to check the traffic on finals when at the hold. It's nothing to do with frequency interference or unwanted RAs, more to do with trying to keep the airbrne units working as efficiently as possible.
At quiet airports it's probably not such a problem, of course, but consistency of SOP is quite important so perhaps the recommendation is about encouraging 'good habits' for when you do visit somewhere busier.