In a perfect world you wouldn’t have to think about stretch percentages and fabric content when working with knits. You could grab any knit from your stash and it would work the same as all the other knits when making the same pattern.
Unfortunately that isn’t the case, many times you have to make some adjustments to a pattern even when the fabric you are working with is one of the listed fabrics. What it comes down to is that all knits are not created equal.