I am using the caps to keep dust out.I have 3 fans running constantly in my rack.( Seems everything I own runs very warm.)I did notice lots of collected dust on those rca jacks.
I also sometimes re-configure some of my ever changing system.I have actualy pluged the right RCA cable into the wrong jack on my reciever.With the plugs I will elimate pluging into wrong jacks, and save myself time and embarrasment.