Quote Originally Posted by Eric
... I understand WHAT a balanced (TRS) vs. unbalanced (TS) signal is, and roughly what a balanced line does (subtracts out background to eliminate noise, I think). However, when and where these are used, why it would be important for a computer audio interface to have balanced outputs, and how this relates to stereo vs. mono are all resultant questions.
I think I went over this before when you were wondering how to connect & use your ME-50 with 2 amps or an amp & a mixer...but here's short course review of the applications or TRS vs. TS:
RE: Audio Interface, any type
Balanced line (terminating with TRS or XLR connectors) will provide a signal less susceptible than an Unbalanced line (TS) to picking up hum and signal 'noise' - in short, a cleaner, truer signal. This is especially true, even a critical need, if the line has to carry the signal more than 10-12' from output to input.
RE: Stereo vs. Mono
Besides being a connector for balanced signals, TRS is used to carry a stereo audio signal via a single cable; most common example is found with stereo hedphones. In this use, the 3 conductors carry L, R and Ground. In other words, 2 Hots (+) and 1 Cold (-).

Another use for TRS is for an 'Insert' or 'Stereo-to-Mono Splitter' cable, usually a 'Y' cord with a single 1/4" TRS plug (Male) or jack (Female) that takes the In & Out (for Insert use) OR L & R, and this is then split to (2) TS plugs or jacks, one for each individual signal. Insert Cable use is most common to 'Send & Return' an Effect device signal To & From an audio mixer's individual channel or Main.

You can use the same Y cable to send a headphone Out jack's stereo signal from an amp or cd player to 2 individual inputs of a mixer for independent handling (processing) of the L & R sides of the signal.

TS connector cables can only carry Mono or Unbalanced signals. The T is the Hot (+), the S is the Cold or Ground (-).