The concept of Aggregates in Domain-Driven Design is based around the need for business invariants that must be maintained with transactional consistency in a system that is generally eventually consistent.

Overall, you have to learn to love eventual consistency, but small portions of the domain should absolutely be clustered together around transactional consistency needs that are absolutely necessary.

Check out "Implementing Domain Driven Design" by Vaughn Vernon; chapter 10 in particular talks about this.