Why ever use CachedGauage in Dropwizard Metrics?
Quoting the same link you added:
Cached Gauges
A cached gauge allows for a more efficient reporting of values which are expensive to calculate
What if your metric takes around two seconds seconds to calculate, or even minutes? Would you calculate every time the user request the data? Makes sense to store on a cache.
Such metric isn't what I would call real time because updating itself takes more time than rendering the information for the user. The metric is outdated already when it finishes it's calculation.