If you delete image files from disk without telling the Catalog: Lightroom not only retains previews and cached data of various sorts outside the Catalog (1:1 previews will eventually expire and be cleaned up) but also keeps hold of thumbnail images inside the Catalog, and of all your editing both global and local, plus other matters such as virtual copies and membership in Collections. These images will continue to show up inside the Catalog in searches of various kinds and when browsing the collections and folders panels. Each image (and the folder) will show a marker to indicate source file not currently findable by LrC.
But LrC cannot distinguish whether this image inside the Catalog is now permanently orphaned - or, just temporarily separated from its source e.g. while an external disk is unplugged.
IMO a far better idea to clean up inside the Catalog and to have the source files deleted from disk as part of doing so. That of course loses all possibility of being able to come back and adjust any editing further.
So as a planned occasional task, one might decide to periodically archive off chunks of the Catalog along with the related source files, into other storage. That's if you want your main storage and your main Catalog kept relatively lean.
Perhaps highlight (say) everything from 2022, "Export as Catalog" to a completely separate (just) 2022 Catalog on an external disk, with copies of all the relevant source files alongside (tick selected images only, tick "include negatives") making that 2022 library selfcontained; then you can bulk remove all these same 2022 images out of your main Catalog - choosing Delete from Disk.
Deletion using the Catalog works file by file on disk, but does not delete the containing folders from disk. So this process will not incidentally sweep up any files that were not imported to LrC. For example: exported JPGs usually do not show in the Catalog, and so are none of its business.
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