Why do you add the ingredients in sequences when stir frying?
Stir frying is a relatively quick cooking process.  Different ingredients often have different cooking times.  You add ingredients at different times so that the longer cooking ingredients will have time to cook and be ready at the same time as the shorter cooking ingredients.  If you have ingredients with approximately the same cooking times, by all means, add them together. Also, however, sometimes ingredients are added in stages so as not to reduce the the temperature of the cooking vessel/environment too rapidly...so that it can recover, and remain at a high temperature.  This would be less of a concern in a restaurant situation, where more powerful burners are used.