It would be useful to display the durations in the Work overview table of related recordings.
e.g. to detect potential duplicate recordings to merge (or recordings that should not be merged), or detect wrong relations between work and recording, or missing durations on tracklists...
I wrote a userscript to add it on the fly, and I know @jesus2099 did it too in one of his scripts (I don't know how many people find it useful). Both have to use the web service for an information which could be provided server-side at no cost.