The "apples" use case is when you want for lack of a better description a Grafana chart out of it. (E.g. the cluster cpu load, "we're getting X page views per second", etc).
The "oranges" case is when every data point matters, and I think that this particular case is not so much about time series, but logging, where a log is a "time series" technically speaking. Here of course you're talking massive amounts of data which you want to do your best to optimize and it's a hard problem. It's not a _time series_ problem, it's a problem of storage. Splunk (sorry, can't think of a better example ATM) doesn't describe itself as a "times series database", and yet it's addressing that very problem of horizontally scalable write-intensive storage. So is hbase, cassandra, accumulo, bigquery and all their friends.
In my experience the best solution is to use two separate systems one for each case. Because there is absolutely no value in a "disk used" measurement every millisecond - aggregated to once a minute (or few) is perfectly fine, and retaining the original data is not needed and you'd be a fool to build a Cassndra cluster to handle it. On the other hand if I'm recording equity bids and asks, well then I better record every point forever.