This also does not preclude adding charges later. They can promise reduced sentencing as opposed to no prosecute.
What is being learned is something we should have understood at the outset: That battling a deeply entrenched political and governmental establishment that has the explicit or implicit support of half of the population and most of the large financial interests in a nation is no easy, straight-line thing.
You will retreat often and need in all cases misdirection and subterfuge in order to battle such an establishment. Leading with your chin or making a full frontal assault will simply result in your own defeat. And you cannot afford to lose even a small battle. What if Comey’s defense lawyers find one person on the jury who will not convict no matter what the evidence is? Who has lost then? Where is the momentum then? The indictment is not the final victory, in fact it isn’t really a victory at all. The conviction is the victory, and the burden of proof - proof that will convince even the jury members that hate Trump with a white-hot passion - is on the prosecution. Always remember what the victory really is...and what failing to achieve it really does to the overall effort.
These are the true lessons to learn before engaging in such a battle.