Lightroom is taking up far too much space on my hard drive

juliao32908813  wrote Can anyone suggest why the local library file is so large, and secondly, what would happen if I just deleted the file? Would I just loose my smart previews?

You should only ever do this if your library shows it is fully synced to the cloud! If it hasn't yet, you can lose raw images. Remember that uploading on most normal broadband connections can take a very long time as the connections are asymmetric (much higher download than upload speed). On a top-tier cable internet connection you typically only get a 5 megabit upload speed. 100 GB on such a connection takes 45 hours if you are able to saturate the connection constantly. So your 100 GB left might actually be raw files that haven't fully uploaded to the cloud yet.

Secondly Lightroom CC automatically manages the local storage but is fairly sluggish at it. It will take it a while to realize it doesn't need the raw files on most of these before it starts deleting them locally. Patience is appropriate.

When you import images into LRCC they are first copied into the LRCC "local space" (the default would be the local library file, though if you have chosen a different location for locally stored originals they would be copied there). Once imported and uploaded, the local copy is not usually immediately purged.....some space management is built in to the app which will manage the local files in accordance with various factors, but gradually over time those originals should be purged if you have chosen NOT to store a local copy of the originals.

Note, however, that even though you may have chosen to store a copy of all Smart Previews locally, LRCC will still download a copy of the original (if it exists in the cloud) whenever you zoom into 1:1 or you start to edit an image.

If you delete the local library file, LRCC will rebuild it from the cloud when you next start the app, but in that situation that initial tranche of originals probably wouldn't be re-downloaded, just the thumbnail and smart previews.

I have a similar amount in the Cloud and my library file is approx. 10GB.

I imagine it's because you have recently imported en masse and some of that space will be purged locally.

However, you may want to check the size of your local Photo Cache in the preferences as well to see what value it is and obviously double check that Store a copy of Originals locally is not on.