There are limitations to what expendable addresses can help with
I'm a long time advocate of using expendable addresses for as many things as possible (and then making sure you can turn them off). However, yesterday's incident of junk email as a cover for worse also shows some of the limitations of using expendable addresses, because they wouldn't really have avoided this situation.
The first way they wouldn't have avoided the situation (of having a flood of junk email sent to someone to distract them) is that generally expendable addresses in all of their forms still funnel into your actual mailbox. Some people sort some expendable addresses into low-priority places, but you're unlikely to do this with the email address you use for things like notifications from your financial institutions. You usually want to see those right away, not have them hidden away.
The second way they wouldn't have avoided the situation is that if someone wants to unleash a flood of email onto you to distract you, it doesn't necessarily matter what exact email address they get their hands on. All they need is some email address that goes into some mailbox that you look at regularly. It would be better to get the actual email address you use with your financial institution, but for drowning a bit of signal in a lot of noise, often many email addresses will do about as well. It doesn't even have to go to the right mailbox, just one that will cause you to drown in the volume.
(Certainly this would be the case for me. I would have an easier time of sorting things later and perhaps not missing signal amidst noise with my extensive collection of expendable addresses, but in the heat of the moment, if you clog up my inbox it doesn't really matter how.)
The one part of this sort of flood that expendable addresses will help with is the longer term aftermath. One of the iron rules of email addresses is that once some people have their hands on some email address, they will never stop emailing it. After a flood, obviously a lot of people have some email address of yours and a certain percentage of them will keep emailing that address forever. If the address they have is an expendable address that you can turn off, you can at least make them go away.