It depends on whether you delete the files from Uplaodcaer after you move them to your bucket. The “custom storage” feature is not a full replacement to Uploadcare storage. It allows you to connect a bucket to your project and copy files to it with REST API or automatically. If you delete your files after you copy them to your S3 bucket, we won’t count storage, but you won’t be able to deliver them via our CDN, and such features as image/video/document processing will be unavailable for these files. It may be ok for some use cases that don’t require delivery and the above features, however, there are ones that require using our storage.
There are other ways to optimize your costs. Drop us a line at firstname.lastname@example.org and tell us a little about your use case so we can see what we can suggest.