Once, you get a call from a B-School for an interview, it's only the (Interview + AWT) Performance that matters. CAT Scores also do matter, but not to a great extent.
Most Colleges have almost 40% weightage on Interview, 10% on AWT & 30% weightage on CAT Score.
If you've really low CAT score, it might impact your Final Selection. Having a relatively bad Score won't make much of a difference.
For instance, Getting a IIM A interview call at 97%ile when everyone else get a call at 99.50+ile will impact your final selection to some extent.
But, getting a IIM A interview call at 99.00%ile when everyone else get a call at 99.50%ile won't make much of a difference in your final selection.
After you get a IIM Call, don't be bothered about low academic scores in Xth, XIIth & Graduation. They don't really matter in final selections. If you've a really low score in Graduations, you might be quizzed on it in the interview. Be prepared with a convincing reason for that.
Thus, once you get a IIM call with decent CAT scores, don't neglect the WAT & make sure your interview goes well. These both are the only thing that would impact your selection.
Note:
FMS follows a unique selection criteria, with CAT score taking up 85% weightage. So getting a 99.50+ile will only give you a realistic chance of conversion.
IIM Bangalore is the only top B-School which gives high weightage to both Work Experience & Past Academics in the Final Selection.