They are not just ornamental, they can really help reduce noise. My situation is somewhat unique, but here's what happened.
From the Rowland Concentra tape outs there's a single ended Discovery cable going into a pair of EVS Ultimate Attenuators/Cardas RCA to XLR adaptors into an Apogee Rosetta A/D. The output of the Apogee goes via a balanced Discovery cable into an RME Pro96 card via the RME supplied pigtail. The pigtail has both RCA and XLR input/outputs on one end and a D style computer connector on the other. The RCA I/O is unused and I cover them with Cardas caps. The other day while converting vinyl to digital I noticed that there was a large amount of noise on the input signal. After much investigating I realized that one of the Cardas caps had fallen off and once replaced the noise vanished. The residual noise level on the input meters of my recording software dropped from -38dB to -54dB.
As I said my situation is unique, but the Cardas caps proved a real problem solver for me.
