Not much. But people who wear clothing in the desert are less likely to get heat stroke and may slow down dehydration just a tad (because sweat on cloth does a kind of evaporative cooling thing; white cotton is really good, synthetics tend not to work as well in that environment).
The differences at higher temperatures (in terms of survival) are small though.
And as to Amboy Crater, I read that the black rock in those narrow, reflective, maze-like mini-canyons radiate heat to the point that it gets to 160F. No one survive that very long. It was something like 120F or more in the parking lot the day the Schmierers stepped out of the car, IIRC (I think they got there mid to late afternoon - people often think it will cool off after noon, but in the desert it really starts to warm up exponentially at noon, compared to morning, the peak temperatures are usually around 4 pm).
The walk to the actually crater is about a mile, maybe 1.5 miles. Even half a mile in that kind of heat (160F along parts of the trail??!?) would result in rapid impairment. A person would normally turn back almost immediately. I suspect they realized their predicament too late and he went for help after she collapsed. My oven's lowest temperature is 120F and frankly, that's too hot for me to touch comfortably much less be inside, I'd retreat immediately. But tourists are often determined. I've gone for a quick walk in 118F in the shade (in Death Valley, just had to put my feet on the ground at Badwater - maybe 10 minutes total). I was aware that I had to go back to the car even though I was very excited (heart rate was up, all of that) and wanted to stay longer.
The family hired Drone-up to find Mrs Schmierer:
https://dronelife.com/2018/09/12/th...up-search-and-rescue-mission-at-amboy-crater/
