Looking for tax experts (CPAs and lawyers) to comment on dependents

I am interested in information from tax lawyers and CPAs regarding the definition of dependents and what this means for filing taxes. I am looking for information on: 1. Who is considered a dependent by the IRS? 2. What is the tax benefit of having dependents? 3. Can tax filers still take exemptions for dependents in 2018 under tax reform rules? Thank You Requirements: CPA, tax lawyer, or other credentialed tax professional.