We many see routes.xml file with the same name of frontname and id. what if it is both different?

<?xml version="1.0" ?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:App/etc/routes.xsd">
    <router id="standard">
        <route frontName="hello" id="world">
            <module name="Bilal_HelloWorld"/>
        </route>
    </router>
</config>

frontname is used in URL construction e.g) http://domain/hello/index/index this URL search routes.xml with the frontname hello. Once it reached the controller, the controller searches the specific layout with route id world (world_index_index.xml).

Simple formula: route frontname used in URL and route id used in the layout.