That is a good question, it depends on the situation.  If your deck is high off the ground and is only attached to the house on one wall, the posts should be in the ground, to provide lateral support.  There is an extra cost involved in the concrete piers; however your posts will last a lot longer

 If your structure is less than 108 square feet, is not more then 24" off the ground, and is not attached to the house,  a permit is not required.  However, getting a permit and having it inspected is the only way to ensure your deck is built to minimum building code standards. Having said that, minimum is only that, the bare minimum. Consideration to increase the post, beam and joist size, would add strength and stability to your deck. If you choose to build your own deck, or choose to have it built by someone, a permit should be obtained. If you do not, there could be problems down the road.

If you’re living in a new home, the building inspector will be around for the next two years at different points. You will get caught. If you’re lucky you may be just asked to excavate your footings, to check the size and depth. If you’re not so lucky you may have remove the entire deck. If and when you go to sell your home, a deck that is built with no permit could actually bring down the value of your home, rather than add value.  A building permit will cost you about $65.00 and will take five to ten business days to be issued, so plan ahead.

It is my opinion that the entire deck should be screwed together with the exception of perhaps the support beams. By screwing the lumber together you will have far fewer squeaks and if the need to replace a deck board should arise, you will be able to do so in an easy manner. Nailing with an air nailer is faster and can be used on the understructure to save some cost, but the deck boards must be screwed

As a rule it should be attached to ensure that it remains stable. When one or more side is anchored to the wall, the deck should remain motionless.  When a small amount of movement is given to the deck that is when things start to magnify. Just like an old wooden chair, eventually someone ends up on their butt.

However, if the deck is less then 24 inches off the ground it could be built on deck blocks to save some time and money. Keep in mind that a deck built in this manor will have movement due to the freezing and thawing of the ground. The farther away from your home the more frost there will be in the ground. Over Time you will see that the deck will tilt one way or another.

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