@cdevroe For spoofing attacks, start here:
https://en.wikipedia.org/wiki/Man-in-the-middle_attack
Now, when you bring this up to most IT pros, they'll say "But, that's so unlikely, and the attacker has to be in a special place on the network.".
But these attacks can take place anywhere along the chain, from browser extensions to on-the-wire to caching, to CDN, to destination infra.
There's also another class of attacks it prevents, but it's complicated, I'm on vacation, and it won't fit in a toot anyway. 😄