Testing or swatch testing yarn is the best way to know how a yarn will behave.
No one wants surprises after spending money on yarn for a large project and then finding it doesn’t perform as envisioned.
A swatch is not only for gauge, but also for how it feels and maintains its’ shape.
I wash my swatches as they will be handled in real life.
You may notice that the yarn has a bit of thick and thin in the strand and how it shows up in the fabric. This may be need to be considered in a larger item. The yarn is a Wool 40%/Mohair15%/ remainingAcrylic/Poly mix.
It appears that one of the fibres in the mix, either was dyed separately, or absorbs the dye differently and appears darker in colour. A dye expert will know the how and why.
To my eye, the fuzz from the mohair obscures the patterning.
Usually, I don’t knit a scarf as a swatch, but did so, only because I had a very large quantity of yarn. Overall, I think it will make a very nice sweater. Perhaps, by using it 2 stranded.