The main advantage of hitting fairways is you don't risk going into thicker rough with poorer lies.
Finishing on the fairway always means that you can attack the green. Going into 30/40 rough or worse, which is always a possibility when you miss the fairway, usually means attacking the green is difficult, although not always impossible.
That being said, I'm possibly judging that when playing from the legend tees. Hitting a long iron from the rough isn't the best thing to be doing.
I very rarely use anything less than a driver from the tee anyway, recently I prefer to hit a punched driver if there is a water/hazard risk from going to far.