In Transformers: War for Cybertron - Siege, Megatron wanted to 'eliminate' the Autobots by using the AllSpark. Therefore, Optimus Prime devised a plan to obtain the AllSpark before Megatron did and take it off Cybertron with the Ark through the space bridge.
At the end, though, in a battle with Megatron, Optimus Prime was forced to throw the AllSpark into the space bridge hole (thus moving the AllSpark off Cybertron without use of the Ark).
Why did Optimus Prime still take the Ark through the space bridge afterwards instead of destroying the space bridge? Wasn't the mission already completed by moving the AllSpark away from Cybertron, and thus keeping it away from Megatron?
What is the effect of moving the AllSpark off Cybertron for life on Cybertron (besides stopping the plan of Megatron)? It seemed to have been suggested that the AllSpark was needed in order for life to exist on Cybertron?
Now that the War for Cybertron trilogy has ended I can answer these questions (in some degree).
Prime probably knew that moving the AllSpark away from Cybertron would have a negative effect. Therefor moving it away was a temporary action (to avoid the genocide plan by Megatron) and moving it back (after Megatron was defeated or gave up the plan?) was the next mission.
Episode 6 of Kingdom showed a Cybertron not capable of sustaining the current generation of robotic life without the AllSpark. All transformers who were stranded on Cybertron died (though new ones emerged afterwards in different forms: Maximals and Predacons). Prime probably didn't know the dependency between the AllSpark and Cybertron in full extend (and all resulting death were therefor him to blame).