Are you referring to mailing lists for newsletters or letting people subscribe to your feed by email? The latter is quite useful because Medium doesn't do a great job of surfacing people I want to read. I follow only 345 people, most of whom I will read if I see something from them in my feed. There are a handful or so of people I want to read whenever they publish. Most of them have turned on the setting for Promote Subscriptions which allows me to ask to be notified of those stories. Without that, I hasve to hunt them down.

I would strongly suggest turning that on. For your real fans, it's extremely useful.