Backlogs affect your profile,but honestly not that much. You can have low grades but strong extra curricular profile or have strong justifications for backlogs and still make it through.

Saying that, more than 2 backlogs shows that you are consistently inconsistent and if you qualify for interview stage you will surely be hard grilled for this. So be very well prepared about it.

baklogs in the subjects which would have a direct impact on the CGPA which ultimately would affect the admissions to IIMs as a candidate with a lower %ile but higher CGPA gets much more preference than the other one with high %ile and very low CGPA.