I recently heard a podcast by the comedian Kevin Hart. In the early 2000s, when he was an unknown and social media didn't exist, he would have a sign-up sheet at his shows, where people could enter their names and email addresses. This way, he'd maintain an email list for each city.

Each time he scheduled a return appearance in that city, he'd send out an email letting people know the date and time of the show and a link to buy tickets.

Today, people build their followings on social networks that barely let you even post links to your own site (Instagram). Had Twitter/IG/FB existed back then, people would have no way to maintain independent contact lists.