Spike solutions are appropriate when:

A.
a specific technical needs to be answered, stopping work on the spike as soon as it
answers that question.

B.
there is insufficient time to refactor, but there is a need to resolve a specific problem.

C.
the business requirements are vague or inadequate for an iteration.

D.
a technology is understood well and has been used for a while, but needs a problem to
be debugged.