A ball lying on the fairway doesn't allow much margin for error when compared to hitting off a tee or mat. Thus, confidence level is lower when hitting from the fairway...doubt and negative thoughts come creeping in. Hello bad shot!! Hitting your 4-iron (layup) will likely result in consistently lower scores because you can pick the best spot from which to play your 3rd (chip) shot onto the green and roll it close to the pin...hello birdie!
Personally, I can no longer hit a 7-iron 150 yards...I can hit 6-iron 140 with roll-out. So, I typically am hitting 3 onto the green (par 4 holes). Getting better at chipping has helped me have more shots at par, and occasionally roll in a chip from 10-15 yards off the green for a birdie. This crucial part of the game is where the pros win championships ($$$$$).