What are the advantages and disadvantages to using a griddle instead of a cast-iron skillet?
Yes, you don't have the edge of a pan in the way when going to flip things, but it also means that you don't have a mass of metal there to add as a heat sink, which can help dramatically when pre-heating your pans, as they'll be evenly heated across their bottom more quickly (at least, compared to something of the same material, such as a cast iron skillet)

More importantly, in my opinion, is that without the sides, you don't hold in moist air, so when cooking things like hash browns, you can get a better crust on 'em without steaming them.