Air Canada apologises for bumping youth off oversold flight - father

Two comments from recent articles:

In the US, which provides the best statistics on this matter, the number of people denied boarding — both voluntary and involuntary — was 1.07m in 1999 but declined to 552,000 in 2015, according to the Bureau of Transportation Statistics. Those might sound like large numbers but the 2015 level represented only 0.09 per cent of trips taken by passengers.

(The graphic in that article shows that around 1 in 10,000 people are bumped involuntarily (0.01%).)

Aviation experts note that if overbooking were made illegal, ticket prices would almost undoubtedly rise.

Source:  https://www.ft.com/content/e4cb5744-1e9d-11e7-a454-ab04428977f9

More importantly, unused tickets cause a liability on the balance sheet — the tickets you sold are often still valid, you just don’t know exactly when those passengers are going to show up to try to re-book their seats.

Source:  https://techcrunch.com/2017/04/11/overbooking/

And here's an excellent article about how they calculate the optimum number of tickets to sell:  (Sorry you'll need a VPN here in LOS)

http://www.dailymail.co.uk/travel/travel_news/article-4401096/Experts-reveal-airlines-overbook-seats.html