Masa Serdarevic summarizes a Goldman Sachs report [pay-walled]:
They found that stock markets of recent hosts have outperformed in the year after the Games, local houses prices have tended to rise and that dictators award the most valuable medals. One of the most discussed questions regarding the merits of hosting the Games is whether it’s a net economic gain or loss for the hosts. Obviously, the government spends billions building new venues, on security and "revitalising" rundown areas — and millions of people visit, spending lots of money. But many people also leave the city during the Games, others don’t come specifically because of them, and businesses suffer lost output due to transportation and other problems. Kevin Daly concludes that there will be some gain to the UK this summer but it will dissipate before the year is out.
The Dish 