Not technically. A server runs perfectly well with nothing but a command line. The question is what your time is worth and what you are comfortable maintaining.
Reasons to install one - cPanel/WHM, or one of the lighter alternatives. Creating a site, adding an SSL certificate, setting up email and taking a backup all become a few clicks rather than a few config files. If you host other people, a panel is effectively required, because your customers need their own interface.
Reasons not to. A panel consumes memory and CPU that could serve your application, and it makes assumptions about how the server is configured which can get in the way of an unusual setup. Licensing is an ongoing cost. And a panel is another piece of software with its own security updates to keep on top of.
A reasonable rule: if the server hosts multiple sites or multiple people, install a panel. If it runs one application that you deploy from a repository, skip it and keep the machine lean.
We can install and license a panel for you at provisioning time, which is simpler than retrofitting one onto a server you have already configured by hand.
