I think that many of us have used a Wye incorrectly and gotten away with it! But we never measured the frequency response and distortion problems that the added burden caused.
On the other hand, a long time ago we all had analog 1/4 inch tape recorders. So pre-amps were wired the tape out jack as a properly connected Wye and everything was great until, until that is you turned the tape recorder's power off. Turning it's power off in effect caused the input transistor to act as a diode across the input jack and the distortion on the pre-amps main output went through the roof. The solution was to only make pre-amps with a buffered tape output.
