Greetings, I'm new to ROS and I was following the tutorial on "a gentle introduction to ROS" book. In the chapter about service, author wrote a spawnturtle.cpp and used turtlesim/Spawn service. Before compiling, author reminded to add the turtlesim in the findpackage() statement in CMakeList.txt, also in the < build_depend > and < exec depend > elements in package.xml.

However, I was able to run and spawn my turtle successfully without adding turtlesim in both my CMakeList and package file.

So what is find_package doing exactly in CMakeList.txt file?