Choose custom storage only when company policy requires files in your own bucket, and accept the loss of CDN operations. If you need transformations, keep Uploadcare storage and back up to S3 separately. Test a transformation URL right after switching storage backends.

Context: Official docs (Uploadcare glossary): you can connect your own S3 bucket as custom storage so uploaded files land there instead of Uploadcare servers, but Uploadcare CDN features will not be available. That includes image transformations and adaptive delivery via CDN URL operations. Agents that wire custom storage and keep building transformation URLs get unprocessed originals.