Just went over gaiden again and noticed when Sasuke said his eye powers were back he activated EMS, but previously he had active Sharingan and Rinnegan. Could it be that EMS drain more chakra than Rinnegan (which i find hard to believe), because when he he wasn't at full power he used both Sharingan and Rinnegan, and activated EMS when his powers were back ..
Also, does he need both EMS and Rinnegan power in his left eye (tomoe Rinnegan) to use his space-time tehnique or just Rinnegan's? Kinda confusing.