5×5 is a suggestion for a workout focused on strength. Its a good idea to ensure that you can do the basic exercises in fairly high volumes before you start focusing on harder progressions. So you should be able to do at least 30 clean push ups consecutively before training for one arm push ups. Even when you’re focusing primarily on harder variations for low reps its still a good idea to ensure you have the endurance to do the basics more. Higher reps allows your central nervous system more time to increase efficiency. Mix it up though, don’t do the same thing every time. Group exercises by which ones you can do together without tiring each other out. That’s what I try to do.