The
region
of interest is the area of the composition that is previewed.
Create a smaller region of interest to use less processing power
and memory when previewing, thereby improving interaction speed
and increasing RAM preview duration. Changing the region of interest
does not affect file output, though you can change the size of your
composition and select what portion is rendered by cropping to the
region of interest.
Note: When the region of interest is selected,
the Info panel displays the horizontal and vertical distances of
the top (T), left (L), bottom (B), and right (R) edges of the region
from the top-left corner of the composition.