A ticket buyer is the person who pays for a registration, who is often not the person who attends on the day.
The buyer pays. The holder attends. At corporate events they are frequently different people: an assistant books for an executive, a manager books for a team of six, a sponsor books for guests. Treating them as one person is where follow-up goes to the wrong inbox and badges print with the wrong name on them.
The buyer needs the receipt, the invoice and the refund policy. The holder needs the confirmation, the badge, the agenda, and anything you asked about dietary requirements or accessibility. Sending both sets to the buyer is the most common version of getting this wrong.
If the record is stored against the buyer, a team of six registered by one person looks like one attendee. Headcount, catering guarantees and sponsor reporting all inherit that error, and none of them is recoverable afterward.
Buyer and holder are separated in the Orders tab, so you can see who paid and who is assigned to attend, and tickets can be assigned to the people who will actually use them. See ticketing and registration.