The tool is designed to help advertisers experiment with bid changes and track what would happen if their increased or decreased their bids for certain keywords.
Google said "ACE allows you to perform faster, more accurate tests by executing your experimental campaign alongside your original campaign. By performing this type of simultaneous split test, we can tell you precisely if your campaign changes produce statistically significant results."
The different things you can test include but are not limited to:
- The incremental impact of adding new keywords to your campaign or changing keyword and ad group-level bids
- The value of restructuring your Content campaigns to use more tightly themed ad groups
- The change in volume by using different keyword match types
- The value of using an ad group default bid versus keyword-level bids
Here is a video:
Forum discussion at WebmasterWorld.