My workflow has always been that if I know I’ll be duplicating the object around the model I make it a component. If I know there will be only one, or I’m unsure I make a group.
I tend to default on groups when I’m unsure in order to avoid the Component Browser to fill up with too many items that I know I won’t be reusing.
It should be said that I also keep my Component Browser and Material Browser in list view instead of thumbnail view because I find it too hard to visually find the correct item if I have many similar ones.
Also, when you have Groups, you can right click them to make them components - but not vice-versa. If you want a component as a group you need to open the component, select all, group it, then explode the component - yuck.