valueIsNumeric string with string value

[checkforants]

I use NumberFormatBase with props
{ "value": "12.0012312300001230655",
"valueIsNumericString": false}
somehow it changes value to 120 012 312 300 001 230 655,0000000000000000000
but documentation says that i should pass valueIsNumericString = true only if thousandSeparator is '.'
I do not t use thousandSeparator, please explain me how it works and why