Exactly.
I mean...if these boxes exist it means that they have their use.
Yes, they break ground loops (which may be necessary to remove hum), and they allow balanced lines to be used which improves immunity from externally induced noise, especially needed with long cable runs or many cables running parallel or electronically noisy environments.
You know...you can also play guitar with a speaker cable instead of instrument cable...it works
And if you did so in an interference-free environment the sound quality wouldn't suffer at all.
The lack of shielding on a speaker cable would result in less shunt capacitance, thus less loss of highs compared to some guitar cables (like the cheap Viper brand patch cables I have kicking around).
Also reamp box can convert balanced signal into unbalanced signal with almost the same level (1 to 1, at least for Jensen`s schematics or modified ProRMP), while without reamp box there will be 6 db reduction in most cases, if I`m understand right.
If using an unbalanced line out, then there's no signal loss at all.
Using balanced line out for an unbalanced signal, it depends.
Some balanced line-outs have signal only on the hot side (impedance balanced), some have signal on both hot and cold.
(In both cases the common-mode noise rejection happens if a balanced connection is used, provided the impedances on both hot and cold are the same.)
If you took signal only from the hot side for an unbalanced connection you'd get 6dB more signal if it was "impedance balanced" because the whole of the signal voltage would be on the hot side.
Whereas if both hot and cold sides of the oputput were driven, half the signal would be on the cold side, and you'd lose it unless you used a transformer (or an electronic differential summing stage).
But this assumes the output level is calibrated to the same as the input that was used for recording.
(I'll add that the cold side outputs of a lot of interfaces are driven by an inverting unity-gain opamp stage. These have signal gain of -1, but noise gain of 2. So they double the total signal level, but add twice the noise of the non-inverting output driving the hot side. It's not a tragedy to throw the cold side output away if the hot side alone will give you enough headroom.)
