Key to the construction of a well-paved and stable driveway is the gravel and sand base. This layer provides more even and flexible support for the asphalt or concrete poured on top of it. You'll find that many paving companies construct the base and pave the driveway within a few days or faster. What that process hides is settling, when the base layer literally settles down much like soil. This is a necessary process to ensure the integrity of the paved surface. You have two options for making sure the base settles. One is to let it settle naturally, and the other is to have the paving company compact it mechanically.
Why the Base Needs to Settle
First, yes, the base does need to settle. When sand and gravel are first poured in, there's lots of air trapped between all the grains and pebbles. Over time, that air works its way out or is pushed out, and the surface of the sand and gravel starts to become uneven as some areas sink faster than others (the sinking is just the particles moving due to the air working its way out; the surface isn't actually sinking below ground). If asphalt or concrete had already been poured on top, the settling would have cracked the asphalt or concrete or created hollow spaces under the surface that would have cracked the minute a vehicle drove over them. By letting the base settle first, you end up with a stable, well-supported top layer.
One Option Is Natural Settling
You could let the gravel and sand settle naturally over time. And there are companies that prefer to do this instead of mechanically compacting the base. The advantages are that the natural settling will be more thorough than mechanical compaction, and you won't have the noise that you would from the equipment used in mechanical compaction. The drawback, however, is that natural settling can take months. You have to have a lot of patience and be able to leave the driveway alone for a long time.
But Machine Compaction Is Faster
Machine compaction involves rollers that press down on the gravel and sand. This is a much faster process and can shorten the settling time to a day or two. This allows the paving company to pave the driveway shortly after constructing the base, and you can have an almost-finished driveway that is usable. The driveway will still need to cure and then be sealed, but even that won't take months. The drawback to mechanical compaction is that you have to trust that the paving company will get all the air out of the sand and gravel base. There's always the risk that something will be left behind, but mechanical compaction usually works very well.
If you need a driveway constructed, call a residential paving company to ask about their process. Be sure to verify how they let the base settle.