1 Daf Yomi was not invented by Rav Shapiro or the Chernobyler Rebbe it was in fact the Chortkover Rebbe zya.
2 For me who is busy working all day it is alifeline. No i do not understand or remember every word but when things come up in my other limmudim such as Chumash Rashi I remember some related gemorrohs from the Daf quoted by Rashi in chumash and the experience is exhilarating!
3 It leads on to other limuudim such as Halacha like you correctly suggest which are important and mussar etc.
4 The Keviyus/regularity is very important