Lots of info in a search.
Stock and big tune, usually enough fuel available.
Larger injectors and big tune, usually or always not enough fuel available.
Not enough fuel leads to low fuel pressure which gives less power and most importantly can damage expensive injectors!
So that is the simplest explanation. Most people that are concerned run a fuel pressure gauge. Fuel pressures under 45 psi for extended periods can be dangerous to the engine, although it really becomes an issue as it dips much lower. So, if you don't plan on pushing the power up too far, you will be fine on a stock fuel system. I still have mine in place, but I will be upgrading in early April to a 6.7l pump system.
