I try not to use any herbicides (2-4D) or insecticides. Some of my neighbors have allowed their lawns to go, so I get the dandelions and crabgrass from them.
I will use some Scotts with pre-emrgent to minimize the crabgrass in a few weeks once all the snow is gone and I rake the lawn out.
I use milorganite and throw alfafa pellets on the lawn. Also use some fast calcium to balance Ph. I do spot spray the dandelions and have some Scotts I got on clearnance last fall for a few bucks a bag if I want to add some quick nitrogen. But have used the milorganite and alfalfa to feed the soil. Get the grass thick and cut high, water deep.
I once got sod webworm on a section of lawn, so I sprayed that, but more reactionary. If your always doing the 4 step programs your slowly killing the soil.
Mine is full of earth worms so that is a good sign it isnt a toxic waste dump, note I am not a greenie, just try to use some common sense.