“So the work we did was all for nothing?”
You have been working on a project for a few months at work, and it's almost finished. Your coworker just told you that a high-level director in the company wants to change part of the project, which means that you will have to re-do several weeks of work. You say this because you're annoyed that the work you did won't be used in the final project.
So the work we did was all for nothing?
Start a sentence with "So..." when you want to re-state or summarize what someone said:
You can also use it when you want to point out the effects that something will have, like in this example:
A: I'm so sleepy. I'm going to bed now.
B: So you're not going to help me clean up?
"All for nothing" describes work that you did, which didn't have an effect or won't be used. In the example above, the speaker did a lot of work that won't be used in the final version of the project. Here's another example:
They banged and banged on the door for hours, but it was all for nothing. There was no one there to hear them.