Exposure is a nondestructive editor, meaning it does not change your original photos when you make edits. Exposure’s edits are kept in sidecar files stored near your photos in an Alien Skin subfolder.
Compared to photos, sidecar files are very small. Typically around 5-50 Kilobytes (KB) each.
Edits that use a lot of brushing or spot healing will be larger. Sidecars for these files may be a few hundred KB.
To put this into perspective, RAW files are commonly around 10-50 Megabytes (MB). There are 1000 Kilobytes in a Megabyte. With this in mind, the sidecar files take up about 1/1000th or 0.1% of the space used for photos.