I never thought about this before but today when I looked up a flight, there was a message that displayed only 1 seat available at this price. On some airline websites if you look up a flight for 1 ticket you get a lower fare because there is only 1 seat left for that price. However, if you search for 2 people its a higher price for both seats even though there is 1 seat left at a lower price. So in that case it might pay to purchase 1 ticket ahead at the lower price and then the order the second seat separate at the higher price as opposed to purchasing 2 at the same time for a higher price each. Makes any sense? Sometimes there might be 3 tickets left at a lower price and you want to order 4 tickets etc.
Good point Rob! You don't want to end up separated. Although 1 flight where i purchased 3 seats together we ended up separated and I didn't even notice until I was boarding. Turns out they changed the plane and reassigned everybody. Lucky for me there was a row with 3 together so they fixed it.