Things that can go wrong if the operating system's space storage hits the wall (many from first-hand experience): * Software can start randomly misbehaving and crashing. * The browser might crash and lose the precious session, e.g. Samsung S Browser. * Firefox Mobile and Chrome Mobile tend to crash on full storage, but without session loss. * Brave browser: Not tested on low storage yet. * The virtual keyboard software might suddenly *forget* custom words. * Your browser might randomly delete browsing history (experienced with Firefox) * On your mobile phone, some app might reset its settings and lose some data due to writing errors. * A text editor that fails to save the file and uses direct clobbing for file saving might overwrite the text file with a 0 byte file. * Low remaining storage leads to aggressive file system fragmentation. * Some mobile apps might refuse to run in first place (e.g. Samsung's precluded media gallery software), despite technically possible. * Software slows down due to restricted ability to use spare space storage for data caching. If I missed a point, or if you would like to share your experiences, feel free to leave a comment. I hope I could help you.