Atwood LawnCare

The short answer to this question is “nothing, if you use the right materials.” The lawn cannot tell the difference between a quality liquid or granular application.
The more involved answer goes to the question of what exactly is being putting on the lawn. Some people feel that a granular product is automatically a “slow-release” fertilizer. This is not always the case. There are many formulations of granular products that do not have any slow-release capabilities at all. If you go to a garden center and look at a fertilizer label, you may or may not see a nitrogen source call WIN. This is water-insoluble-nitrogen and is a measure of any slow release capabilities. Many, many granular products do not have any WIN present.
The converse is true as well. Just because it is a liquid application, does not mean it is all “fast release” fertilizer. There are many quality slow release liquid fertilizers that are used extensively. Companies who make liquid applications can find quality slow-release products to use if they choose to do so.
One big advantage to liquid applications is that only one pass has to be made over your lawn to fertilize and apply weed control. If a granular product is used, an extra trip is needed to apply the weed control. Seldom is a granular “weed & feed” product used because it is not as effective as a liquid application.
Another advantage of granular products is if a specialty problem develops that requires a special treatment plan. Using the flexibility of carrying several different types of products on their vehicle, a trained technician can decide what is best for your lawn conditions, if something special is required.
So don’t judge a book by its cover. There are good reasons why Atwood LawnCare uses both liquid and granular products. Ask a few extra questions about what will be used on your lawn to decide what is best for your lawn.