What happens if I include 'Joint Gift' on the post payment form?

If you include 'Joint Gift' on the post payment form it will still count as two donors on the campaign totals but

Joint gift donors are not included in email notifications. For matches and challenges, joint gifts typically count as two donors, and the secondary donor is included in match or challenge progress in most cases. The only exception is when a match or challenge is directed to a specific class year: if the joint partner’s class year is provided and does not match the targeted year, only the primary donor counts.