Use case: Any languages where it is helpful to pull additional information from a second or third resource, e.g. to look up root word of conjucated/declensed forms; or to see more example sentences.

When reading Czech texts in LWT, I use LWT's second dictionary for extra example sentences, and I kidnapped the third one for a resource that provides grammatical information (http://prirucka.ujc.cas.cz/, for case, number etc.) This is very convenient because I get a better idea of how else a word could be used and review grammar at the same time.

One could use this similarly for Spanish, by adding http://www.linguee.es/ for example sentences and http://www.spanishdict.com/conjugate/tradujese to get verbs analyzed.