Answer – Pending Response
Does anyone else login to your site? Do you allow visitors to your website to register and create user accounts? Or are you the only person who is allowed to login to your site?
Response:
It will be a membership website, so yeah I will have users registering and creating accounts.
But how is it related to my question?
Answer:
Because Members to your website will need to be able to access their WP Profile on your website. The WP Profile is located in /wp-admin/.
It is not necessary to block Subscribers/Members from your /wp-admin/ area because WP uses Roles to restrict users capabilities. Ie an Administrator user Role can do anything and a Subscriber/Member Role can only do very limited things.
Typically Membership Plugins and Themes create a custom Profile area where users are sent to. That could be in the /wp-admin/ backend or somewhere else depending on the Membership Plugin or Theme.
Membership Plugins and Themes are typically designed to restrict/limit access to things. So to answer your question, since you have a Membership Plugin or Theme you are already restricting/limiting access to your site and the /wp-admin/ area.