Zend certified PHP/Magento developer

Magento 2 Is it good idea to use ES6 syntax in custom modules?

Some developers suggest to avoid ES6 syntax in JS files to keep the entire codebase unified with a single JS standard.
After examined vendor folder I saw some modules use es6 (For example vendor/vertexinc/module-tax/view/base/web/js/form/element/custom-option-flex-field-select.js).
So, that’s why I have doubts about the statement about avoiding using es6 syntax.