My clients are charities. They have to be very careful about committing spend when running donation appeals. We generally start off with a smaller budget, gauge potential success, then revise the budget as the campaign progresses.
Depending on what they’re advertising, a conversion can be cheap ($15) or very expensive. It’s a competitive sector. ROAS determines long-term spend. Imagine how many charities are currently running ads to get donations for Beirut! And we’re always comparing channels, because Facebook or other ads might give better ROAS.
Problem is, as you point out: the lower the spend, the longer it takes to get enough data to base decisions on. And if they aren’t getting enough conversions regularly, you won’t be able to switch successfully to the better bidding strategies.