For example if you want to set an explicit exit code. Calling python scripts will usually result in an exit code 0 after the script is run. If you want to set a different exit code for example 1 to indicate some error occured you can do that via sys.exit(1).
Same thing applies to other languages of course.
The C++ Core Guidelines are a set of tried-and-true guidelines, rules, and best practices about coding in C++
From the submission: >> “Within C++ is a smaller, simpler, safer language struggling to get out.” – Bjarne Stroustrup > >The C++ Core Guidelines are a collaborative effort led by Bjarne Stroustrup, much like the C++ language itself. They are the result of many person-years of discussion and design across a number of organizations. Their design encourages general applicability and broad adoption but they can be freely copied and modified to meet your organization’s needs. > >The aim of the guidelines is to help people to use modern C++ effectively. By “modern C++” we mean C++11 and C++14 (and soon C++17). In other words, what would you like your code to look like in 5 years’ time, given that you can start now? In 10 years’ time?