The short answer
Usually, after a check. Might hold something you care about. Look inside before removing it.
What is it?
The “Smart Previews.lrdata” package next to a Lightroom Classic catalog holds compact DNG versions of your photos. They let you edit, and export at reduced size, while the originals are offline, for example on a disconnected drive. They are much smaller than raw originals but add up across large catalogs.
Let you edit photos while the originals are offline. Lightroom rebuilds them only if the originals are connected.
What happens if you delete it?
Lightroom can only rebuild them when the original files are connected. Your edits are stored in the catalog, not in the smart previews, so they are kept either way.
How to remove it properly
In Lightroom Classic, select the photos and choose Library › Previews › Discard Smart Previews. Alternatively quit Lightroom and move the Smart Previews.lrdata package to the Trash.
Quit the app that uses it, then move it to the Trash. Empty the Trash when you’re sure.
Before you delete it
If the originals are on a drive that is not connected, or no longer exists, smart previews may be the only editable version you have: keep them.
How MoreRoom helps
MoreRoom recognises this item and labels it “Review first”: it shows what’s inside, its size and last use, so you can decide. Nothing is removed without your say, and everything goes to the Trash first, with Undo.
Frequently asked questions
Is it safe to delete Lightroom Classic Smart Previews?
Usually, after a check. Might hold something you care about. Look inside before removing it. Lightroom can only rebuild them when the original files are connected. Your edits are stored in the catalog, not in the smart previews, so they are kept either way.
Will Lightroom Classic smart previews come back after I delete it?
Yes. Lightroom can only rebuild them when the original files are connected. Your edits are stored in the catalog, not in the smart previews, so they are kept either way.
How do I remove Lightroom Classic smart previews properly?
In Lightroom Classic, select the photos and choose Library › Previews › Discard Smart Previews. Alternatively quit Lightroom and move the Smart Previews.lrdata package to the Trash.