Feature summary
The files uploaded to UploadWizard would be held in some kind of temporary storage that is cleared after a certain amount of time (10 days for example).

The file storage could work like a sort of network folder where you can upload the files and finish them at a point in time that is different from uploading.

Use case(s)
Currently UploadWizard stores the files (I guess in some kind of cache) while uploading. When you upload too many files at once or have a slow internet connection and thereby your uploads take too long, UploadWizard "forgets" the files and the upload process results in an error. The same happens when you take too long to finish your file descriptions.

If you upload only a hand full of images and have a fast internet connection, it's not a problem as you hardly exceed the time limit before your data is deleted.

However, I have a metered connection that is sometimes rather slow which causes all sorts of problems when uploading. When I have a bad (slow) internet connection so it takes rather long to upload images so I lose time here. I usually upload more than one image at a time as my time for this activity is rather limited. This results in a larger pile of files that I upload and write descriptions for. If I don't split them up into groups of a couple of images, I always error out on the upload process and have to restart again. This is not an ideal situation as I have a metered connection.

Benefits
If you error out on the upload, you lose time for no really good reason. If you have a metered connection, you also lose a portion of your monthly data budget.

In sum such a feature would help users with slower internet connections to be more effective when uploading files to Wikimedia Commons.