1. Yahoo has official email ids which no longer work (but were functional in the past). Are these also up for grabs? Or, are some email ids "more equal than others"?
2. Websites with paid access. There are people who sign up and do not access these sites for a long time. If the person who signed up with his Yahoo email id no longer uses it (the email id) now, there is the danger of someone claiming that email id and then using the "Forgot password" option on one of these paid websites. Most of them send your password to your email id, or send a link to reset it.
Boom. You now have access to their personal information (and possibly credit card/bank details) as well.
Edit: Even free websites quite often store personal information, for that matter.
2. Websites with paid access. There are people who sign up and do not access these sites for a long time. If the person who signed up with his Yahoo email id no longer uses it (the email id) now, there is the danger of someone claiming that email id and then using the "Forgot password" option on one of these paid websites. Most of them send your password to your email id, or send a link to reset it.
Boom. You now have access to their personal information (and possibly credit card/bank details) as well.
Edit: Even free websites quite often store personal information, for that matter.