A lender's policy is effectively mandatory in practice, since most lenders will not fund a mortgage without one, and it pays out to the lender, not the buyer, if a title problem surfaces after closing.
An owner's policy is optional and protects the buyer directly against the same kinds of problems, an old lien that was never discharged, a boundary error, or fraud on the title, that would otherwise come out of the buyer's own pocket to fix, and it typically adds a modest amount on top of the legal fees, $800 to $1,500, a lawyer charges to close.
Ask your lawyer whether an owner's policy is included in your closing package or priced separately. Get your hand-reviewed valuation from Joel Dyck.