You don't need Lot Adjuster to use them (though it's a really handy program to have!), but Mootilda says you should always note when you've used it to shrink a lot, maybe so the downloader is aware that the lot is built up closer to the edges than would otherwise be allowed? That means if you delete an outer wall or floor by the edge, you won't be able to rebuild it since the game normally won't let you build all the way up to the edge. Does that make sense?