At any step in your funnel,
Anywhere you look at your marketing funnel, you need volume.
The natural question to ask is: how can I get more volume for the same cost? This question spawns a lot more of other questions.
If you have an ad optimization system (and/or group of media analysis), this is the area where they will spend most of their time. How can I make my ad creatives more engaging? Which platform, device, time of the day, group of people should I target to get more volume for the same price? All in favor of reaching more people, faster, cheaper.
If you have a $1k daily budget, and your audience size is 1M users. Can you reach them all in one day?