This is especially true in newer housing developments where a six-inch layer is the rule. If you live in the country or an older neighbourhood, you may have more to work with. Sod removal is hard work, but results are instant. If you don't, expect to spend a lot of time weeding until plantings mature and begin to spread. If you are planting seeds, mulch around seedlings while they are still young.
Lawns get a lot of foot traffic, and compacted soil is the result.
Cultivation will make the soil easier to plant into, and will create pockets of air, essential for plant growth. And the soil probably isn't rich enough to support a garden. Mix in compost and topsoil.