In one post it was written that:
You tend to use the covariance matrix when the variable scales are similar and the correlation matrix when variables are on different scales.
What does scale refer to here?
Does it refer to the units (e.g. physical) that the variable have or merely the numeric value?
Are variables with different empirical meanings in binary matrices on the same scale or not? They only get values 0/1, but the "physical meaning" of 0/1 might differ between variables.