A radalt? I know a few TB20 pilots who have put in a KRA10. I wonder what they use it for.
A radio altimeter is an excellent reminder that you have reached your minimum. Over the years, I had countless incidentens with students and infrequent IFR-flyers who were so busy keeping their ILS needles centered that they forgot to look at the altimeter. In the procedures trainer, I let them continue to touchdown without intervening. You should see their puzzled faces when they suddenly hear the "squeak" sound from the tires (or the "crash" sound if the sink rate is too high or they land beside the runway)! "Why was that?" is the usual answer...
Another use is as a primitive ground proximity warning system. Everybody has heard (or should have heard) about the calculation of "minimum usable flight levels" in non-ISA atmospheric conditions. But how many actually perform this calculation when they fly IFR over mountainous terrain in underpowered aircraft? A radio altimeter ca save your day then. Of course, modern GPS based avionics have a much better terrain warning built into them, but not every little club aircraft has them.