Memberstack has a lot of features for sites with paying members, which might leave you asking: do you have to include paid memberships in your site?
It's totally fine to use Memberstack without asking members to pay.
Quite a few sites using Memberstack offer "free" accounts to clients, employees, prospects, and more. Free accounts are a great way to get folks excited about your content and to prevent users from outside your organization accessing hidden content.
When you create a membership, you'll see an option to make the plan available for free.