Slow release fertilizer combines the characteristics of the organics and the soluble synthetics your lawn needs. Usually this type of fertilizer has a high percentage of nitrogen. Spreading large quantities of fertilizer is not necessary for healthy lawn growth. Slow release fertilizer delivers nitrogen slowly to the lawn. As a result nitrogen does not become available to the plant all at once. Fast release nitrogen can burn a lawn if spread too thickly. Most importantly ometimes a heavy dose of fertilizer can even kill the lawn. This is one of the reasons that many gardeners use a slow release fertilizer. They avoid any chance of damage to the lawn.
They also use spreaders that deliver fertilizer evenly and over a wide area. As a result this avoids concentrations of too much fertilizer in one area.
Several types of fertilizer are available. WIN which means water insoluble nitrogen. Many commonly available lawn fertilizers are actually a combination of soluble nitrogen and WIN. Whether you water the lawn immediately or wait until it rains, there is no danger of lawn burn. The fertilizer is insoluble and will not release quickly.
Many lawn growers prefer slow release fertilizers. They make heavier applications of nitrogen possible. Hence making fewer applications necessary. However, they do not provide a quick green up of the lawn. Your control of greening response is slightly more than with organics.
Use a fast release fertilizer to green up your lawn quickly. However, extreme care needs to be taken to avoid lawn burn. The fertilizer should be spread less heavily and carefully.