Many packages depend on a specific version of electron. As those packages are updated, the version number is updated. As they update the version of electron needed is also updated.
This often leads to a situation where you have an old version of electron that you no longer need. Those old versions stay on your system until you remove them. Eventually, those packages leave the repo and end up in AUR. However, once they hit AUR you are building them from source. Building electron from source brings down a huge repo since it is based on chromium. While it isn’t 50GB, it still can take a long time to clone a repo that large, especially over a slow connection. Once it is downloaded, you then have to build the whole thing from source which also can take a long time.
Removing that old version of electron you no longer need, stops that whole process from happening and leaves you with a normal update.
To avoid that in the future, you should check your system for orphans once in a while with yay -Yc