There are a lot of options when considering putting down grass. Sod? Seed? Sprig? Hydromulch? Each has it's advantages.
If you need your grass fast, this is the choice for you. You can choose any variety of grass when sodding, while seed and hydromulch are more limited. It's great, but its your most expensive option.
Inexpensive, but grow in can be difficult. Seed can be washed or be blown away. You are also limited on the types of grass you can put down.
Sprigging is great if you want to put down a specialty grass at a price lower than that of sodding. The grow in can be a challenge, but with the right experience this can be a great option. The cost is much less than sod, but more than seed or hydromulch.
This is a great middle ground. Grow in still has it's challenges - it is neccesary to water consistently once applied, but the glue and fiber layer hold the seeds and fertilizer in, keeping them from being washed or blown away. You are limited on the variety of grass you are choosing, but unless you need specialty grass, this a great option.