Throw the baby out with the bathwater
Definition 1 of 1
Pro Tip 1/3Metaphor Origin
The phrase comes from a time when water was scarce, so the baby's bath was last, and dirtiest. 
Learning the origin can stop you from throwing out the baby with the bathwater when discussing resource waste.
Pro Tip 2/3Negative Connotation
The phrase often implies a careless or thoughtless mistake, not a deliberate choice. 
When you fired the team to cut costs, you really threw the baby out with the bathwater.
Pro Tip 3/3Cautionary Advice
Used as a warning to consider the value of what you're getting rid of. 
Don't throw the baby out with the bathwater by deleting old files without checking their contents.