It implies that there is a high level of confidence that the event will occur, even if it hasn't happened yet.
Here are some examples:
* "The deal is as good as done. We just need to finalize the paperwork." This means the parties involved are confident that the deal will be completed.
* "Once the team secures funding, the project is as good as done." This implies that securing funding is the final hurdle before the project begins.
* "The election is as good as done, with the candidate leading by a huge margin." This suggests the election is a foregone conclusion, although the official result may not be in yet.
The idiom emphasizes the speaker's confidence in the outcome, even if some formalities or minor details remain to be finalized.