2" makes a huge difference.
Laying your fly 2" from the bank instead of 4" can mean the difference of having a very productive day or just a so-so day.
River Banks erode and create undercuts in the bank just below the surface. This is a favorite holding spot for fish. It is a great location for ambushing other prey and also provides shade. As a result you must get your fly in very close for the fish to see it.
Get your fly in close and experience an increase in productivity.