When we were small, we didn't want to burden our 2-person development team with needing to integrate against every downstream marketing and analytics tool we wanted to try. Adding segment let our developers integrate once and let our product, growth, and sales folks experiment with whatever tools they wanted to use.
As we've grown, Segment has grown with us. We haven't needed to worry about event volume, or special cases: we can filter events from destinations, or add custom cloud-based logic in Segment [server-less] Functions.
On Segment Functions: If you've got a particularly challenging integration challenge—in our case synchronizing Segment events with Hubspot CRM object properties—Segment also has "Segment Functions" available. We've found it quite convenient generate a single Segment event like "User Updated" and use it to trigger a Segment Function which calls back our application API to get more information, and enrich the objects in HubSpot with a single call. Review collected by and hosted on G2.com.