Scooter and Bob pretty much nailed it. Products with prodiamine as the active ingredient will give you longer weed prevention coverage--normally 90-120 days--compared to Dimension(dithiopyr active ingred) which is more like 30-60 days(at best) The reason you would use the Dimension is if you are planning on doing some fall seeding, you can do multiple apps of it and know that it will be gone from the soil most likely by seeding time(Early Sept). With prodiamine, if you drop it in May, it may last right through Sept, which is great for longer season crabgrass control, but makes Fall seeding more tricky because it will also prevent the grass seed from growing too. If your sod is nice and thick, I would skip the seeding and just do the Weed preventer.