I understand what declarative languages have to offer, but I have not yet connected the dots as to why I would use them. For example, I do not understand why describing a problem is more beneficial than writing a solution to an already understood problem in an imperative language (side-effects non-withstanding).
This is not a discussion about what makes a good application in declarative language. I only want to understand the circumstances and any common, specific project requirements that would make a programmer say “We really should use a declarative language for this”.
As a rule of thumb, I guess declarative programming makes sense when there exists multiple strategies to achieve one goal. Declaratively programming the what rather than the how let the parser/compiler/runtime figure out which strategies is best–it optimizes the execution for you.
Two exemples of declarative languages and optimizations:
The link provided by @verisimilitude is worth reading.