Edge platforms run your code physically close to your users, which can take a 300ms request and turn it into 30ms. For SaaS products that compete on responsiveness, that gap is the product.
What Belongs at the Edge
Authentication, personalization, A/B routing, lightweight rendering. Anything that needs to be fast and cares more about latency than throughput.
What Does Not
Long-running jobs, heavy database writes, and anything that depends on consistent global state. The edge is great for reads near the user and surprisingly hard for writes.
State Is the Hard Part
Edge databases exist, but most are eventually consistent or expensive at scale. Design your data model with the edge in mind, not retrofitted later.
Conclusion
Edge is not a replacement for your origin. It is a layer in front of it. Used deliberately, it can be one of the cheapest ways to make a SaaS product feel premium.