A DPF and SCR delete and EGR block will add mileage (big time), engine and turbo life, and eliminate the issues and cost of DEF. You can delete and not blow coal or add big hp, that's up to you. But your warranty will be blown.
Some state patrols are now looking for the DEF tanks with the mirror - don't remove the tank itself if in doubt. If you live in an attainment area where you have to have your truck plugged in to get your plates, recognize they typically just check for engine codes/lights, and confirm it's a diesel and not a gasser, but check first. Can't speak to the east coast, no idea out there, anything is possible. It's getting harder, but it's not impossible - unless you own an L5P, but that will change eventually, too. How many L5P's are out of warranty from mileage - very few (100k warranty, only out two years).