Don't tell that to a friend of mine, Steve. He went to pull honey last year and due to our high humidity, most it was uncapped. A few weeks later he walked out his back door and all of his hives were roaring. He could hear them 200' away and the out side of the hives were covered with bees. He used small computer fans and solar panels. The fans only come on when the sun is on his hives. Just during the middle of the day due to tree shade. His frames are now capped quickly and he has them on all his producing hives. He has little bearding. He thinks they make a big difference. They probably aren't needed in dry areas but with 80 to 100 percent humidity they help.
I use screen top boards with insulation in the top cover and it helps. I do often have several frames that are not capped but usually due to new nectar in areas that had had some brood it in.
"The fans only come on when the sun is on his hives." well that tells you you are getting solar gain on the hives... try lots of insulation and aluminium foil