Disadvantages of z-buffer or depth buffer

Question

Write down the short note on the disadvantages of z-buffer or depth buffer?

Answer 1

The disadvantages of depth buffer or z-buffer are as:

i)  Doubles memory necessities (or at least) one for z-buffer and one for refresh buffer.

ii)  Memory intensive. Device dependent and

iii) Spends time on rendering the polygons which are not visible.