A Child Theme Confusion

Hello there, I’m trying to get the hang of this, but there is something in the concept of child themes that I can’t really understand:

If I’m using some default theme (2014 for instance) and want to add some plugins that will be extensively used (like visual Composer, or Wp-Courseware, or others)to make my final site… then what should I do? Install them on the Parent theme, and then make a Child theme for all subsequent tweaks,
or
should I leave the Parent Theme with just 2014 (and “default” Plugins…askimet etc…) and Create a Child theme to Install new Plugins and addons to do all my subsequent Tweaks, customisation?

sorry for the so basic, maybe stupid question, but as I said, it’s a bit confusing for me, whether child themes are more designed for purely “aesthetic” safe tweakings (Stylesheets etc…) or should a Child Theme be created whenever you add ANYTHING other than the Original Parent theme?

thank you so much for answers! (It’s been bugging me for a while and can’t seem to have this doubt solved anywhere… So it must be me being stupid).