I'm not quite sure how to answer your question. The "normal" way to use Lightroom Mobile is to import your images using the desktop application on your main computer. Then you create a collection and choose to share that collection using Lightroom Mobile. Then smaller copies of your images are sent to the cloud and you can access them using your android device. Of course, this means that you have to be using Lightroom CC. You must have a creative cloud subscription for this to work.
I'm rather talking about the scenario, where I take the pictures with my mobile phone (Android based). Which saves them into the DCIM/Camera folder. And then import them into the Lightroom Mobile. I'm not interested in importing photos from desktop Lightroom.
From my experience Lightroom Mobile duplicates the photos on the device (taking up space) rather than referencing the existing photos in the file system.
I am not able to use mobile devices very efficiently so I'm not the best resource for Lightroom Mobile. I am providing you a link to a video that might be helpful. I realize it's using the iPad, but hopefully it will give you some better information on how importing to Lightroom mobile interacts with Lightroom on the desktop. Be sure to watch to the end because I think that will answer your question.
I can't help you with best practices, but I can say that Lightroom copies the images. I don't see a way to change this. On my Galaxy S6, they're copied to:
/storage/emulated/0/Android/data/com.adobe.lrmobile/files/carouselDocuments/<random hash>/Originals/<folders by date>