What size previews are you generating on import e.g. standard or 1:1 previews. The previews folder can grow large unless emptied regularly. 1:1 previews can speed up editing in the Develop module but once your editing is complete you can discard them to free up space. LR gives the options to discard after one day, one week, after 30 days or never. It’s not a good idea to have your prefs set to never if disk space is to9 be optimized. I have mine set to 30 days which generally works well. You can check your settings.
From the top menu go to:
Lightroom >> Catalog Settings >> File Handling (tab)
You can also check the size of the Previews.lrdata folder by going to the catalog folder from Finder. The default location is the Pictures folder.