e.g. Bob bought Apple stock for $50 a share back in the day, and sells it for $200/share. He defers his taxes until 2026. Instead of paying capital gains tax on $150/share, the cost basis is adjusted by 15% so in addition to benefiting from the time value of money, future Bob will only be taxed on $142.50 of capital gains. Bob can buy a house in an "opportunity zone" (from scrolling around the embedded map, there's plenty of million dollar+ houses in these areas. There's also lots of sports teams and stadiums in these areas, so maybe Bob buys an NFL team or a parking lot next to their stadium), rent it out for 10 years, sell it, and not have to pay any capital gains tax on the appreciation. Definitely not a bad deal for him!