3 Dimensional geomerty is just an extension of cartesian geometry in an extra dimension which makes it extremely interesting.
Yearly trend The graph shows conveys that for JEE Advanced there had been a kind of alternating trend, where in if questions are asked upto 3 questions are asked otherwise questions are not asked. JEE Mains has a more steady trend, you get nearly 2 questions definitely from this chapter.
Important topics A point in 3-d is represented as (x,y,z), where x,y,z are distances from yz,xz and xy plane respectively.
Questions from this chapter are around the distance between 2 planes, the distance of a point from a plane. It is also important to look at the conditions for interstection of line-line, plane-plane.