Do both with a perma green unit.
I like the flexibility that granular fert offers. I can carry five different types of dry material in my truck, and be able to custom treat each lawn on an individual basis. If you mix up 200 gallons of a high N fertilizer, and come to a lawn that you want a low N fertilizer on, you will have to do one of two things. A. COme back with a different mix, or B, reduce your rate of application. Here is the problem with reducing the rate of application. If you have a herbicide mixed in the tank, you will not be applying enough herbicide, and essentally wasting all that herbicide.
Another thing about spraying is IPM. If you mix up 200 gallons of fert with weed control, then each and every lawn that you treat with that load gets a blanket application of weed control, whether they need it or not. That is not IPM friendly, and wastes money and herbicide as well.
Of course, you can say mix straight fert one day, and fert plus weed control the next, and plan your route accordingly, but that can add a lot of excess travel time in, as well as a few wasted trips.
You will use less herbicide if you are using a perma green unit. You can shut the liquid off if you come to an area of the lawn that is weed free. Try doing that with a spray rig. You use less herbicide=$$$ savings.
I don't generally use fungicides, but I would think that I could use the liquid through my spray tank. There is the cost savings.
I have one of those cheap 20 gallon sprayers nounted in the bed of my truck that I make my mix in for the day. I will then fill the perma green unit up from that. So, my mixing time is greatly reduced.
Another benefit is that you don't have to dedicate a truck or trailer to hauling a apray tank around. You can use just about any pickup to haul your bags of fert, and spreader. WIth a 200 gallon spray rig, well that is a different story. You can also take along the fert that you will need, along with the spreader on your mowing day, and treat the lawn after you finish mowing, saving a trip. That is how you can make the real money.