I've always wanted the ability to remove/filter out/change bad data from a report suite without having to use some scary Data Sources upload to remove data. Some examples of data that would need to be removed/filtered out.
Suppose your website has a spike in fraudulent orders and you want to take them out of the dataset as they are tainting your commerce and campaign data. Today, that is a real pain to do.
Suppose that you are running a foreign ecommerce site and the exchange rate is incorrect and causes your revenue data to be inflated or under-represented. No way to alter the revenue amount.
Maybe you have orders where part of it is cancelled
Perhaps there are pages in your report suite that shouldn't be there and inflating your traffic numbers.