> the shell script is just for convenient of inserting the bin directory into the $PATH so just "python" or "pip" runs the right thing.
Or so any reference in the program you run that launches another binary or loads a DLL relying onnthe environment gets the right one, etc. There are some binaries you can run without activating a venv with no problem, and others will crash hard, and others will just subtly do the wrong thing if the conditions are “right” in your normal system environment.
Another implication of this is that its impossible for 2 mutually incompatible copies of the same package to exist in the same environment. If packageA needs numpy 1.20 and packageB needs numpy 1.21, you're stuck.
Or so any reference in the program you run that launches another binary or loads a DLL relying onnthe environment gets the right one, etc. There are some binaries you can run without activating a venv with no problem, and others will crash hard, and others will just subtly do the wrong thing if the conditions are “right” in your normal system environment.