Reinvent the wheel
Definition 1 of 1
Pro Tip 1/3Avoid Duplication
Use this phrase when suggesting to use existing solutions instead of creating new, identical ones. 
Let's not reinvent the wheel; the accounting system we have is efficient enough.
Pro Tip 2/3Suggesting Efficiency
The phrase implies that time or resources should not be wasted on solving a problem that's already been addressed. 
Instead of reinventing the wheel, we should improve upon the work our predecessors did.
Pro Tip 3/3Express Frustration
It may express annoyance at someone's attempt to do unnecessary work. 
He's reinventing the wheel by rewriting the report from scratch.