when do you need to check if a plugin is enabled/active?

we've got some plugins that are riddled with this kind of code:

controllers :
ActionResult RespondToSomeRequest(){
   var plugin = MyPlugin.GetPluginIfEnabled(); <-- uses code like

  var pluginDescriptor = _pluginFinder.GetPluginDescriptorBySystemName("MySystemName");
            if (pluginDescriptor == null || _pluginFinder.AuthenticateStore(pluginDescriptor, _storeContext.CurrentStore.Id)==false)
                return null;
            else
return pluginDescriptor.Instance() as MyCreditPaymentProcessor;


Services have similar code

Events and overrides similar again... I think payments or shipping ones are subtly different, but I have done some tests and if the plugin is disabled then you can't GET to many of these elements so the checks are redundant in many cases...

I see there is a check like this in some of the built in plugins... but I couldn't see one that used it in more complex scenario (like our integration plugin that sends/recieves data to our admin tool.
...so where DO you need to put this check in?