What does the saying 'Don't throw the baby out with the bath water' mean?

We use this expression when we want to keep the valuable things when we get rid of the things we don't want. It is usually used in the negative to mean that we don't want to throw out the good stuff when we throw out the bad stuff.
Is an old saying which means - inadvertently losing or getting rid of something of value while getting rid of something of no value; making a mistake in judgement; an unintended consequence.