Electrical components are rated on their ability to perform over time as they're exposed to temperature variants...from hot to cold. This also applies to its "working environment".
Electrical components in digital cameras are no exception. The sensing technologies that meter light, the flash regulating circuitry, and ultimately...the image sensor, are all susceptible to performance degradation by being exposed to excessive temperatures...hot or cold.
Knowing what I know about electronics and having spent the last 12+ years of my life testing and designing these types of circuits, I practice a conscience method of letting my camera have some "off time" during a shoot day...either outside shooting swimwear catalog or in a hot studio. It seems anal to some onlookers...but I'd rather play it safe rather than have to keep re-investing $$$ in replacement equipment.