I think the vast majority of well architected software applications will have the property that no component alone is too large to be deployed as a “personal” deployment.

The ability to point deployed personal stacks at a pre-production environment (this is often the default) instead of another personal deployment is a means of breaking the chain of needing to deploy personal instances of every dependency needed to function.

This gives the developer choice. If they are only working within one part of the system, only a single personal deployment may be needed. If the change is more cross cutting, multiple personal deployments could be used (or maybe, the change should be made more incrementally).