When trying to grow an AdWords account, one of the more useful metrics is impression share. Not so long ago, impression share metrics were very coarse, appearing only at the campaign level. Slowly, Google has been revealing this data with more and more granularity. Where this metric is low, it’s very useful to raise bids to capture more clicks. 
There have been four changes announced to impression share metrics. Three are useful, and the fourth would only come in handy for small accounts.
The less useful change deals with separating impression share for display and search at the column level. Only in rare cases would we suggest running the same campaign for these two very different users. This obviously limits the value of the new metric. However, for small accounts, it might prove valuable.
The first change is an increase in accuracy. Details are scant on exactly what this means, but anything that provides more accurate data is welcome. It’s hard to know beforehand if this will generally increase reported impression share or reduce it. RankHammer will provide an update as the change occurs. Google has indicated that it will phase out the old data, so it’s easy to believe that it will be a significant revision.
The next change falls in the category of more granular insight. Time of day impression share will now be provided. This is great news for those accounts that use time of day bidding. It’s a lot more valuable to have high impression share when buying decisions are prevalent. For example, restaurants may find searches near meal time are more valuable than those later in the evening. Fifty percent impression share around noon and nearly one hundred precent the rest of the day might look quite healthy from a blended metric, but would be far from ideal on capturing peak demand periods around lunch. This is a change that will be very powerful for businesses with these key demand periods.
The final change deals with reporting and rules. In particular, impression share will be a metric that can be used to trigger automated changes, or provide specific levels of reporting. A couple of use cases include automatically raising a bid when impression share drops, or picking out groups with impression share that is too low (or even too high). Actions such as this have taken a manual review in the past, which can be time consuming for large accounts.