Playing against the AI is a good way to practice the mechanics of the game (how things work, what to click on, etc).
Playing against the AI is NOT a good way to *learn* the tactics and strategies that will work against humans.
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By playing the AI, you get a feeling for the pace of tech development and when you can expect to be able to field ships of certain types.
By playing the AI, you DO NOT get a better understanding of how to handle early conflict, skirmishes, and full-on wars in a game against humans, because how the AI does those things is entirely different from how humans will do them.