Personally, I have done nearly all of my training and flying from airports near sea level. However, I recently took my father flying in Colorado. Combine that with an air temperature of 85-degrees and my airplane was performing as if I was taking off at 7,000'msl. Samething can happen in the deserts of the West. As they heat up in the summertime, density altitude can push the envelope of safety.
Cold air is more dense.
It provides more lift, your rate of climb will increase, and takeoff distance will be reduced.