Analog summing advantages

In the analog world, there are no 0’s and 1’s, only voltages.
These complex sinusoidal voltages include harmonics and other elements.

Analog summings are producing 1st, 2nd, 3rd etc. harmonics as well as saturation/rounding peaks which makes sound so called warmer, fatter, richer.
It provides headroom buffer zone for harmonics, transients or loud sounds without risking clipping, which result a more dynamic open and wide, depth 3D sound.
When mixing on a computer, many prefer to sum the tracks in the analog domain, which can result in more depth of field and a wider, more defined stereo image. I hear phrases like “more depth and separation,” or “more rounded/warm low end”, bass is round and fat, middles are intensive but pleasant, trebles are nice and silky.

A sound engineer described as follows: the digital mixing is a mathematical summing, for example 1+1=2 (exact 2). When you mix in analog: 1+1=2,05 (because your tracks are summed as sinusoidal voltages) + as well as adding beneficial harmonic distortion the “pleasant harmonics”, rounds, transparency and more spatial depth.

Simply boost up your DAW output Level (master fader) – and you get some “nice” distortion because you’re pushing the summing inputs quite a bit over its nominal level  

read more about harmonic distortion: https://vintagemaker.net/analogsummingmixer/#harmonicdistortion

What is the Headroom?
Headroom is the point “the safe place” where your transients are not damaged.
Headroom is how much room has your audio signal has before it starts to get compressed and distorted.
It provides buffer zone for harmonics, transients or loud sounds without risking clipping, which result a more dynamic open and wide, depth 3D sound.
It provides space for Gentle Harmonic Distortion (harmonic and non‑harmonic distortions – analog nonlinearities)
You know 0db = clipping mess if you go past it in digital, and in analog 0db is perfectly fine and you’ll have like 15-20 db of “headroom”

read more: https://vintagemaker.net/analogsummingmixer/#headroom

In digital and analog audio, headroom refers to the amount by which the signal-handling capabilities of an audio system exceed a designated nominal level.[1]Headroom can be thought of as a safety zone allowing transient audio peaks to exceed the nominal level without damaging the system or the audio signal, e.g., via clipping. (wikipedia)