A well-researched and thorough keyword base is the foundation for a strong search ad campaign.
That doesn't mean it needs to contain every keyword possible. In fact, scaling the size of a keyword base to fit the ad spend budget is important, otherwise a campaign will optimize slowly and likely under-perform.
It's also important to identify keywords that don't have adequate search volume for the PPC campaigns to match to them. It's too expensive, in terms of server capacity, for the platform to match to many "long-tail" keywords. So they declare them "Low Volume" and in effect, penalize campaigns that use them.
Here's how we assemble a good keyword base, through the process of keyword discovery.