I think the best part about this is that it makes it easy to see who is selling your email. That can bring some accountability to these services that collect your email, and supposedly never use it.
In my experience, though, they deny everything when you follow-up.
At one point I started receiving third-party spam to santander_currentacct@[domain]. I contacted Santander, my bank, to ask how that e-mail address had leaked. They insisted that I must have used it elsewhere since their systems were watertight.
I changed it to something like santander_dontspamme@ and sure enough after a few months the spam started. This time Santander didn't even reply to my complaints.
I subsequently moved my current accounts to another bank, leaving £0.01 in several Santander accounts just to keep them open.