Ans. Reality - Advanced is what most prepare for and mains is what
most of them get. (Sorry, no offence)
Technicality - Mains is about solving a problem in 2 minutes
(average), Advanced is about solving problem in 3 minutes
Lessons Taught - Mains teaches you to be fast in solving a problem
whereas Advanced teaches you to have better conceptual clarity.
Methodology - Mains is more about practice whereas Advanced is
more about logic and idea generation.
Result - Clearing mains makes you eligible for Advanced whereas
clearing advanced makes you eligible for admission in IIT.
Lastly , Mains makes you capable enough to be called an engineer
whereas Advanced makes you capable enough to be called an