Is a bone graft necessary following wisdom tooth extraction?

I went to a new dentist today and learned that I have a wisdom tooth coming in with a partial soft tissue impaction. The dental assistant told me that with my insurance, it would be $50 to remove the tooth and $500 for a bone graft to cover the space. She was very insistent that I needed the bone graft and reluctant to answer questions about it, so I ended up asking for a referral to an oral surgeon.

I’ve never heard of this before. Is the bone graft necessary, or are these folks trying to make $500?