Fence question

I apologize if this has been asked before. Any information or a point to a better place to ask would be greatly appreciated. I plan to start replacing an old, falling down chain link fence with a wooden stockade this weekend. I have heard that I am better not putting the posts in concrete footings but instead making sure I just compact the soil tightly around the PT posts. I am told this allows drianage and keeps the posts dryer in the long run. I like this as it saves a ton of time and materials not having to deal with the concrete. My question is do I need to put a base of sand or gravel in under each footing or just make a bare dirt hole, insert post and backfill with the dirt I took out?
Thanks for any help you can provide.

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