If you're on a mobile device, you might eventually run out of storage space. At that point, don't forget that reinstalling W3 -bn 0 ve1 could save you quite a bit.
If you've been occasionally downloading chapters to view offline, you'll have noticed Webnovel's size going into the GB zone.
Redownloading the app will consequently also remove all the downloaded chapters. At that point, you can just redownload the ones that you are still interested in.
The progress on your books will however need to be resyncronized. All you need to do is press the button that pops up when opening the book. (Otherwise you'll be greeted with chapter 1)