I've been thinking "use" and "no" would be of use inside a subroutine to save memory at that time but found out the hard way the "no" did nothing at all to the memory. Probably using "no" will be even a performance hit everywhere over my scripts?

'use' lines are evaluated when your script is compiled, before anything else, so even if you place them in a sub, those modules will be loaded when the script is compiled and before that sub is executed.

You can get round this to only load a module when the sub runs by using require or eval:

sub foo {
    require Module;
    import Module;
}

sub bar {
    eval(use Module);
}
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