Africa seems like it was a pretty good place to be. You didn’t have to worry about being cold anywhere near as much as in Europe, North-ish Asia or North America. The expansion could have happened while staying within warm areas like the Middle-East, India or Indochina. Besides simply having more people and land, were there benefits to going into areas where the cold could be dangerous for long periods of the year?
“Humans” here encompasses all species of the homo genus.
“Cold” here means not just ice & snow but also UK or Netherlands-like weather.
“Benefits” could also include changes to humanity itself as a result of being in a cold environment.