OPeNDAP is a web service for netCDF-CF files. Web services offer you live access without the need to download a local copy, that would only occupy disk space and become outdated. However, for performance issues, having a local up-to-date copy is very useful. This applies even more when you often work in places wwith with low-bandwidth internet connection, or even without wifi, such as public transport. A local copy for temporary use is known as a cache. Remove the cache when you do not need it any more.
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