module.xml the attribute
active="true" is used but I could not find out what difference it makes to use it or not.
<module name="xxxx" schema_version="0.0.1" active="true"/>
It makes no difference, at all. The attribute active="true" was something that was used in Magento 1, and is found, for some reason, in some Magento 2 tutorials, but crucially, never in tutorials from Magento themselves. There are actually usages of it in dev/test modules, (look at the registration of Magento_TestModuleDirectoryZipCodes) but, if your email address doesn't end in @magento.com, there isn't any need to use active="true" in your magento 2 modules.
In fact, I'd advise you not to and it's literally just adding a pointless attribute to your XML node, and given it isn't used, it's going to sure as hell confuse any future developers in your company. How it got there in your code base in the first place is probably looking at an example module.xml and picking out a dev one by accident or following one of these misguided tutorials.