Light Table has problems for non-trivial code anyway. What happens when functions have side effects like deleting files? Most of my code involves networking, especially Android devices talking to http servers providing functionality that has state. Things don't run in isolation, there are databases involved and code can't be called willy nilly.
And a lot of code is about error handling. In addition to the normal path I really need to see the flow through the problems - permissions issues, timeouts, resource limits, service failures etc.