When a campaign isn’t limited by budget, we can often increase the spend without lowering ROAS by much at all.
However, when that same campaign has maxed out its spend (meaning it reached its entire audience), using a lower-spend outbound campaign (such as YouTube or display) can increase brand awareness and introduce your offering to a new audience.
So, we recommend starting these campaigns with a lower budget to see how it affects the overall campaign performance. The main campaign should become more active, thus allowing us to increase the budget.
You will sacrifice ROAS with these new outbound campaigns, so it's best to keep the ad spend low in the beginning to test this.