Most sellers focus on what keywords to target.
But smart sellers also focus on what NOT to target. This is where negative keywords come in.

If your ads are getting clicks but not sales, chances are you are wasting money on irrelevant searches. For example, if you are selling a premium leather wallet, do you really want to show up for low AOV products or keywords having loose intent?

Negative keywords donot just cut waste, it give you set of complete irrelevent kw too which is not at all relevent for your brand. And if you have set of those kws maintained in your list, you can add them next time before launching any new campaigns.