Understanding how your free 20-Gig storage works will prevent any unpleasant surprises in the future.
As an added bonus, Lightroom Classic users who wish to sync images to Lightroom Mobile using Smart Previews now have unlimited storage – free of charge – for this purpose, meaning they can transfer any number of images without hitting that 20GB cap at all! No limits! All free!
What are the main sources of 20GB storage consumption?
mes From Lightroom Mobile’s integrated camera (which quickly fills up if shooting RAW images).
b) Import images from your DSLR or Mirrorless into Lightroom Mobile.
If all you’re doing is syncing images between Classic and Mobile (like I do), you won’t run out of space, because none of that free 20 GB is being utilized!
Robb wrote an excellent piece that covers this in greater depth (here’s that link), but hopefully this helps clear up some confusion, and assist you in better managing any free space (or at least providing peace of mind that you may no longer need to stress over it).