1) Low # of events per users. For example, if you have a lot of anonymous users who don't do many events and leave. In this case, you may have a lot of MTUs but low number of events. True for a lot of consumer businesses.
2) You have a huge scale (10s to 100s of millions of events per day). In that scenario, we support deploying enterprise RudderStack inside your VPC but still managed by us. In this case, we don't have to incur infra/data-transfer cost (and charge 80% margin) so can be much much cheaper. We have a couple of customers in this model. Some choose this for privacy/security reasons.
In normal scenarios too we can be 50% or more cheaper. Unlike Segment, we don't store any data (which is a major cost) so our COGS are quite lower. We use your warehouse for all the CDP features.