The importance of Iago's loss of control is initially to show to the audience that jealousy and evil in Iago caused not only Othello's downfall from valiant to a madman, but also Iago from completely in control of his actions to acting on the spur of things and incidents not ending the way he wants them to. It also shows that one cannot keep foul deeds to themselves for long and that sooner or later people will find out and the risks are enormous.
In conclusion, Iago's different behaviors enabled him to control his victim's fates increasingly effortlessly, helped to manipulate them without even noticing how easily Iago was corrupting them, and in Othello's case how easily Iago had persuaded Othello in believing in Desdemona's infidelity.
The importance of all these actions were to highlight to the audience how effectively one person could be trusted, an "honest" person and how easily it is to bring down the people around you but undeniably it ironically brought down the villain - Iago as well, even though it was not what he had planned.
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