What is it?
Small cell technology typically supports a couple dozen simultaneous subscribers, and is designed to deliver coverage over a smaller area (similar to a Wi-Fi access point). Adding more coverage requires installing more nodes. Each individual small cell requires its own backhaul connection to the network source, while an entire DAS network requires only a single backhaul connection.
Why use it?
The primary benefits of small cell are that the technology can be deployed faster than DAS; is less design-intensive; and has lower up-front costs.
Small cell and DAS are solutions for different needs, and can be viewed as complementary technologies. The most appropriate solution for a given application should suit the details of the project. Both DAS and small cell can be used together to deliver a lower cost of ownership and easier deployment.