Yeah, my interpretation is that it's for situations where you would normally prefer to use a fake email (joeblow238998324@gmail.com) but can't because of the verify link.
I think this was a nice experiment and still usable for many services.
guerillaemail+myusername-mypassword@gmail.com
As others have clarified, only for complete throwaway accounts obviously. I tested '-' and '!' and those characters appear acceptable as the delimiter. ':' gives a very strange error on send when using gmail.com. Also imagine you'd lose some letter casing along the way.
Really just a fun and terrible idea!