When and where is the “chmod +x script.sh” command really required?

When I started the LEARN BASH SCRIPTING section of Learn the Command Line, they told me I needed to run chmod +x script.sh so the script could execute, but in this module: https://www.codecademy.com/courses/learn-the-command-line/lessons/learn-bash-scripting/exercises/conditionals
I was able to execute script.sh without typing that.