Use or Importance of $\Rightarrow^*$ operator Particularly, there are 2 variants of $\Rightarrow$, one is $\Rightarrow^*$ and another is $\Rightarrow^+$ which are used in derivation of strings using the productions of the grammar.

As stated here, when $\Rightarrow^*$ is used, it means derive in 0 or more steps and when $\Rightarrow^+$ is used, it means derive in 1 or more steps.

What I don't understand is what is the use or importance of $\Rightarrow^*$ operator?. It just replaces the head of the production with the head itself.
Is it that the $\Rightarrow^*$ operator is just there to define operators in some standard way or it actually differs in the way it is used as compared to $\Rightarrow^+$?

Also, while deriving strings, to skip some obivious steps(like replacing multiple non-terminals in a string with their respective terminals), should I use $\Rightarrow^*$ or $\Rightarrow^+$?
It is false that $\Rightarrow^*$ " just replaces the head of the production with the head itself". $A \Rightarrow^* B$ means that the sentential form $B$ can be obtained from the sentimental form $A$ by applying any number of productions (which might be $0$ or more than $0$). 

For example if your grammar is $S \to a$, then all of the following are true  $S \Rightarrow^* S$, $S \Rightarrow^* a$, and $S \Rightarrow^+ a$, while it is false that $S \Rightarrow^+ S$.

If you are deriving strings and applying at least one production per step then both $\Rightarrow^*$ and $\Rightarrow^+$ are correct. The latter is more specific since it implies the former (but not vice-versa).