Twin Set?

So monozygous or 'identical' twins are not genetically identical! It has been demonstated that, on average, 5.2 early mutations occur once the egg has 'split' into two potential individuals (https://www.theguardian.com/science/2021/jan/08/identical-twins-are-not-so-identical-study-suggests). So why is this important? In the past, studies on monozygous twins have been used as the benchmark to distinguish genetic ('nature') from environmental ('nurture') effects on a variey of physical (e.g. susceptibility to cancers) and mental (e.g. being diagnosed as suffering from depression) conditions. Recognition of the, albeit small, genetic differences between 'identical' twins, means that one cannot be certain any differences between the two individuals (say, in one being autistic and the other not) are consequences of environmental factors alone.