In practice it is a problem if your device stops getting iOS updates but you would like to continue using it for web browsing.
Old example, my iPad3 was working perfectly fine as a casual web browser until the day iOS updates stopped just as javascript ES6 spread around the web. Developers everywhere replacing "var" with "let" (Steam website for example). iOS Safari on iPad3 suddenly stopped rendering Steam pages, which up until that day I enjoyed browsing from my couch with the only tablet I owned at the time.
Old example, my iPad3 was working perfectly fine as a casual web browser until the day iOS updates stopped just as javascript ES6 spread around the web. Developers everywhere replacing "var" with "let" (Steam website for example). iOS Safari on iPad3 suddenly stopped rendering Steam pages, which up until that day I enjoyed browsing from my couch with the only tablet I owned at the time.