Hi, 
those are properties that we add to elements in order to apply some changes to them. 
Basically, if only few element need a property we add style="..".. but when we want to apply it on many elements Or when we want to target an element in Js files, then we can add a class and all its properties will spread to all elements that have the class.

In your example, the classes are used in Js : sale_product_configurator/sale_product_configurator_views.xml

we have: o_sale_product_configurator_edit or o_sale_product_configurator_add

these classes are necessary and they are used in sale_product_configurator/static/src/js/product_configurator_renderer.js

hope this helps.