The belt circuit is a major design consideration for your conveyor. Generally a simpler circuit means longer belt life. This would make, in most cases, the Simple Conveyor Layout the preferred method for maximum belt life.
A simple conveyor layout can be used if discharge of products over the drive sprockets is acceptable.
An 'S' Drive conveyor layout can be used to obtain a smaller transfer diameter at the discharge or where discharge of products over the drive sprockets is not desired.
Whenever possible the drive should be positioned so that the loaded portion of the belt is pulled, particularly with longer conveyors.