The optimum temperature for PLA is 210 degrees centigrade. However this temperature varies with different PLA filaments. It can vary from 180 degrees centigrade to 230 degrees centigrade depending on the make and type of the filament. The best source for this information is the Data Sheet for the filament. This data sheet contains all the details regarding the material properties of the PLA filament, ranging from melting temperature, feed throat temperature etc.
Regarding your question of ease in printing in higher temperatures. This is a wrong notion. The temperature has to be in the optimum range or around the optimum range. Higher temperature causes extruder to malfunction.
Why is it the optimum temperature? This has to do with the thermal properties of the filament. As mentioned earlier, optimum temperature differs from filament to filament. According to the temperature profile of each filament the temperature of operation varies. Making it necessary to choose the type of filament as per use and accordingly make changes to the temperature settings as necessary.