With the egr your truck is literally eating its own crap. It would be like us taking a massive dump and then eating it, the egr delete stops this and just sends the recycled exhaust straight out the exhaust pipe instead of circulating it back into the engine, hence the name exhaust gas re-circulation (EGR). Like mentioned above, your cooler will eventually fail like mine did at 37,000 miles and blow white smoke due to leaking coolant. The egr will also lower your engine temperature and avoid any further problems like blowing your head studs or gaskets. It's like 80% of the 6.0ls problem fixed. Highly recommended if your state does not do emissions checks every year, otherwise you can get a huge fine. If you decide to purchase the upgrade, all the guys on the forums running 600+ hp pointed to this kit, make sure you get the up pipe.
IPR EGR GEN2 Delete Kit with Up Pipe & Gaskets for all 2005-2007 Ford Powerstroke 6.0 will fit F250, F350, F450