Many clients like to be able to edit or create documents or spreadsheets within their Apps on the go on an iPad or iPhone.
Currently, it is not possible to upload these.
Moodle Mobile could be added to the iOS share sheet so that within another app or a view of files (.doc, .xls, .pages, .pdf etc...) you can share that file with Moodle Mobile. Moodle Mobile then asks you where you want to put this (Private files or within a particular course) and that file is then uploaded as a resource.
Likewise, It may be an idea to see if Moodle Mobile itself could let you "Upload Files" and be able to select a file from iCloud Drive. Though I'm not sure how much of this is possible due to the sandboxed nature of apps.
(I've gone for iOS specific as I don't know Android. However the same functionality should exist for Android.)