This. Down in central Florida, when they used to have a citrus industry, on cold nights they'd put thousands of them out throughout the groves. The cumulative heat produced supposedly helped to keep the frost from damaging the crop, since that area doesn't usually experience cold much lower than right around the freezing mark. If it was windy, the smudge pots weren't necessary, as the frost was unlikely to settle, anyway, and if a drastic low was expected, like into the low 20's or lower, they'd turn on the sprinkler systems to encase the fruit and trees in a comparatively warmer 32° coat of ice.