Is hiring a digital marketing agency really worth it for startups?

Hey folks,
I'm in the early stages of launching my startup and I keep hearing that working with a digital marketing agency can make a big difference in growth and online presence. But I’m not totally convinced yet—there’s a lot of conflicting advice out there.
So I wanted to ask: Has anyone here actually hired a digital marketing agency when their business was just starting out? What kind of impact did it have? Was it worth the cost?
Also, what should a startup really expect from a digital marketing agency? I’m talking realistic outcomes—not just vague promises of "more traffic."
Would love to hear any personal experiences or tips before I commit to anything. Thanks in advance!