Bigger action set pieces are usually what is shot on IMAX so that when you are in an IMAX theatre, the picture expands and the clarity increases. To my knowledge, no blockbuster movie has been shot entirely on IMAX cameras yet, so I'd doubt they'd shoot the whole movie that way.
Speaking of IMAX, are there literally no 15/70 IMAX theatres at all anymore?
EDIT: I was beat to it I guess.