The default android emulator is ridiculously slow and resource hungry, which makes it an impractical solution.
How can I speed up the default emulator?
Granted - Android emulator is slow. But the upside is that when you develop an app, you instantly see where it is slow/lagging, while on last-gen 1GHz+ devices this might not be apparent.
Also, when I test my apps I run them on 2G network to see the delays and where they need to be optimized. If I'd only run them on 10Mbit+ WiFi then delays would not be noticeable.
When developing you have to plan (and test) for the worst conditions, not ideal ones. So, in a sense, slow emulator is actually helpful ;)