The Internet gives many things. But none that are permanent. That is about to change. Librarians got together and recently launched https://perma.cc/ which provides a permanent link to stuff.
Why is link rot important?
Here’s an excerpt from a paper by Gertler and Bullock:
“more than one-fourth of links published in the APSR in 2013 were broken by the end of 2014”
If what you are citing evaporates, there is no way to check the veracity of the claim. Journal editors: pay attention!