Object cloning is done so that subsequent actions on the object are applied purely to the "detached replica" (cloned object) and not the original object.
By not cloning, in other words just declaring the preexisting object as a new variable, you enjoy (or not) the effects of using a reference variable. In all usages and for the life of the two variables, all actions on either variable -- will be "shared" and will affect both objects.
There is more to this story regarding "shallows copies" and "deep copies", but I'm probably not well positioned to speak on this. If there are fringe cases that defy the truths that I have stated above, then I am unaware of them.
I've extended this Stack Overflow snippet to show the marriage between non-cloned objects, and the independence of cloned objects. Demo
I have an example where cloning is beneficial during the process of building a mysql query with separate Joomla database objects. Scroll to the bottom of my answer at https://joomla.stackexchange.com/a/24148/12352