Does marking unwanted email as spam really do any good?

on YAHOO! for instance, you can mark spam email as spam. does it do any good? will it stop it ?

Does marking unwanted email as spam really do any good?
No it won't stop they have thousands of email addresses and just use another one. All we can do it mark it Spam and delete it.
Reply:It WILL slow it down, but it will never stop it, sorry. You should see what your inbox would look like if you did NOT do it!