This is what the campaign actually spent instead of what might have been budgeted for a 30-day period.
This KPI is very important to take into consideration when reviewing properties to see if a campaign has either overspent or underspent and needs immediate attention.
*An example of a campaign underspending - Daily budget is $81.66 = $2,450/mo
There can be many reasons for this outcome, and a few are listed below:
The campaign is out of funds
The campaign end dates might not be correct
The daily budget is inaccurate
The CPC max bid might be too low
Impression share might be too high, limiting the campaign
Google implemented auto spending using the entire budget for the month
Regardless of the reasoning, any overspending or underspending will result in optimizations needed.