The only time you will need
this term is when acceleration plays a big factor with your robot. If your robot is really heavy, or gravity is not on it's side
(such as steep hills), then you will need the integral term.
The sampling rate is the speed at which your control algorithm can update itself.
To increase sampling rate, you want an even faster update of sensor readings, and minimal delay in your program loop.
The Line Following is a kind of the robot contests to vie running speed
on the line. I build a tiny line following robot which can run on the
desk, moving the key board aside will do.