Nowadays you almost never need to care about CGI for new work. CGI is cool to learn to understand the basics, and I do encourage you to dig into those nuts and bolts behind the scenes. But modern frameworks like Mojolicious are much nicer to work with for new projects.
Using CGI (or rolling your own CGI toolkit) for new work in 2018 is not the shortest path toward getting a good product completed. But learning CGI will help to gain a deeper understanding of how internet protocols work now, and have evolved over time.