Like (I suspect) a lot of folks here, I no longer use gmail (or yahoo, outlook, etc) for email.
But I still check those old accounts once a month or so. And yesterday was a good example of why.
There was a message from Parallels: "Confirm access to your Parallels account from an unrecognized web browser."
Welp, that web browser was Chrome on a Windows 10 machine in New York City. And was not me.
Obviously, I changed my password immediately. I hadn't used Parallels in over a decade -- on logging in, my license was literally from a version released in 2011 -- but the old account still existed. Could someone have really done harm with it? Probably not, but I also don't know how many old accounts from software and websites I haven't used in a decade are still around. And how many of those might offer some of my personal info.
I don't have my old email accounts forwarding, since the last thing I want is for my current email to be associated with them, and the second-to-last thing I want is all the spam that would come with it. But I also don't want those accounts gone, because I want to know if any when old accounts get compromised before finding out the hard way.