Intuitive meaning of complex time domain signal representation (quadrature sampling) I saw What is the meaning of imaginary values in the time domain?.  

My question is about I Q samples as recorded from an SDR receiver (e.g. RTL-SDR).

My understanding is that we can call these I Q samples a complex time domain signal and these can have both non-zero real and imaginary components (the question I linked above is talking about zero imaginary part in the time domain).

Is there an intuitive explanation of what is the meaning of this type of complex time domain signal?

I can think of taking a simple case of an input sine wave of a frequency below the sampling frequency which would make the IQ signal's phasor rotate with the frequency equal to the difference between the input sine wave's frequency and the sampling frequency thus allowing to unambiguously reconstruct frequencies up to (but not including) the sampling frequency from the IQ samples.

But I'm struggling to extend this special case to an input composed of several sinusoids of different frequencies.
One common use of the IQ data from an SDR is to feed them to an FFT.  The upper and lower halves of an FFT result indicated different relationship between the (real) cosine and (imaginary) sine components of the complex FFT result. The direction of rotation of each complex component tells the rest of the signal chain whether the complex component is an upper or lower sideband of the assumed center tuned frequency of the IQ SDR data stream.

The quadrature component in the IQ input is what allows the two halves of an FFT result to not just be redundant complex conjugates of each other (which they would be given a strictly real input, no Q or zero Q).  Thus allowing separating the upper and lower sidebands as independent spectrum.

Also see: https://electronics.stackexchange.com/questions/39796/can-somebody-explain-what-iq-quadrature-means-in-terms-of-sdr/99617#99617