The ACoS Target indicates the ACoS goal you would like to achieve in the long run. Varying it will have direct effects on bids per click (CPC), impressions, position in search results, and campaign profitability.
You can increase it at any time if you want to increase visibility, or decrease it to focus on profitability.
We recommend that you choose a Target ACoS of 5% below your break-even ACoS. For example, if the break-even ACoS of the product is 30%, then set 25% as the target ACoS.
How do the bids per click vary if I change the ACoS Target?
At a high level, bids per click are set up according to a formula similar to this one:
So for example, if you increase the Target ACoS from 20% to 30% (+50% increase) then bids per click will increase by +50%.
Increasing bids per click will make your product rank higher in the search results, but the higher cost per click could increase your ACoS, risking that you won't be able to financially support your campaigns in the long run.