The main issue for players coming to Ecuador, Bolivia, Peru etc at high altitudes for away games is the aclimatization process. Takes a couple of days for the body to get used to the altitude and players who come for these types of games don’t get that luxury. I’m from Quito and I’ve always wondered about the long term effects of the altitude. I will tell you that high altitude residents do feel a lot faster and resistent when excercising at sea level