请教一下，文件的 7 种同步或备份方式，分别适合什么样的场景？

原文为 Dropbox 安卓第三方客户端 Dropsync 博客中的一段介绍他们所支持的 7 种不同的同步方式。

User's Guide-MetaCtrl

1. 双向同步
2. 仅上传
3. 上传后删除
4. 上传镜像
5. 仅下载
6. 下载后删除
7. 下载镜像

Sync Method: Two-Way

New files and modified files on one side are transferred to the other side. Files deleted on one side are also deleted on the other side. After sync is finished the two folders are exact copies of each other. This is how the official desktop clients work (but not so with their Android apps).

Sync Method: Upload Only

Files newly added or modified in device are uploaded to the cloud. Files deleted in device are not deleted in the cloud. Uploads are remembered and being done only once. If the uploaded files are later deleted in the cloud they will not be uploaded again unless modifications have been made to the original files in device. No changes are made to files and folders in device.

Sync Method: Upload Then Delete

New files in devices are uploaded to the cloud then deleted from device. After sync is finished no files are left on device side. Think about it as Move Files from device to cloud.

Sync Method: Upload Mirror

Make the cloud folder an exact copy (mirror) of the folder in device. All files in the device folder are uploaded to the cloud. Files deleted in device are deleted in the cloud. Changes made in the cloud folder are overwritten. Extra files in the cloud folder which are not in the device folder are deleted.

Sync Method: Download Only

Files newly added or modified in the cloud are downloaded to device. Files deleted in the cloud are not deleted in device. Downloads are remembered and being done only once. If the downloaded files are later deleted in device they will not be downloaded again unless modifications have been made to the original files in the cloud. No changes are made to files and folders in the cloud.

Sync Method: Download Then Delete

New files in the cloud are downloaded to device then deleted from the cloud. After sync is finished no files are left on cloud side. Think about it as Move Files from the cloud to device.

Sync Method: Download Mirror

Make the folder in device an exact copy (mirror) of the cloud folder. All files in the cloud folder are downloaded to device. Files deleted in the cloud are deleted in device. Changes made in device are overwritten. Extra files in the device folder which are not in the cloud folder are deleted.

以云相册的同步逻辑来说，国内安卓厂商的云相册似乎都是双向同步，Google Photos 的处理方式应该称为备份，是第二种仅上传的方式，已经上传到云端的，本地删除云端仍然保留。

那其他几种同步或者备份的应用场景呢？