I totally agree with Robert. It kills me to see people scalping their lawn all the time. the three inches is key year round.
I have yet more advice to add.
Also very important, LEAVE THE CLIPPINGS ON THE LAWN! They are 10% nitrogen.
When starting a lawn, buy a named variety, so when you go to re- seed or fill in spots that have died, you won't have a patchwork lawn.
Cut with a sharp blade, set it to 3-4'', as leave the clippings, and your lawn will be lush.
