Not much really. Not at first. The real impact would be post Covenant War, with Voyager's tech being very useful in rolling out the advancements made during the conflict and reverse-engineered Covenant/Forerunner tech, along with aiding in further development.
The arrival leaves them adrift at superluminal velocities, at just the right distance (very, very far above!) to impact something vital (like, say, a ship carrying critical spartans or AI or something) at an inopportune moment. Voyager is destroyed, with total loss of crew, along with a great deal of collateral, and the resulting lack of nail sees the entire human front collapse, leading in the eventual xenocide of humanity by Covanent forces.
