Functions independently or taken over from other scripts?

Hi, I was wondering in general about this, but provide example would be the best way how to put this.

If I would like to use function (that has been already made in some script before) for new script, is better to just tell the new script “hey, that function already exists, in that one!” or just copy paste it and use it again?

Example: Cuff function from policejob to other job

You know, because of optimization reasons… :v: