Python packages can be installed in an "editable" or "in-place" installation mode, where instead of copying the package's code into a virtual environment, there's a pointer to the source directory instead. This allows any changes made to the package source to be reflected instantly in every virtual environment where the package is installed this way. This video demonstrates how useful and powerful this can be for Python developers, as it becomes far easier to evaluate changes made to a package without having to reinstall it each time you change it.