The web is very volatile, from a day to the other a website can be broken, modified or even shutted down. As a result, as time goes on, a part of the URLs you pasted into your Obsidian's vault are very likely to not return anymore the content you had seen at paste-time. Leading to a direct loss of your sources and inspirations.
The Web Archiver plugin solves that problem by taking snapshots of all the URL's you will paste in your Obsidian vault.
More preciselly, each pasted URL will be sent to archiving providers (like Internet Archive), which will indefinitely store the content you've seen at paste-time, allowing you to browse that one even if the original website have been broken, modified or shutted down.
Mention this study : https://perma.cc/63AP-6EHJ