When to use xargs when piping?

Question

I am new to bash and I am trying to understand the use of xargs, which is still not clear for me. For example:

history | grep ls

H

Answer 1

GNU Parallel can do the same as xargs, but does not have the broken and exploitable "features".

You can learn GNU Parallel by looking at examples http://www.gnu.org/software/parallel/man.html#EXAMPLE:-Working-as-xargs--n1.-Argument-appending and walking through the tutorial http://www.gnu.org/software/parallel/parallel_tutorial.html