Today i had (small) insight on how to explain the usage of measures to a customer. In my opinion, there are three layers where we can store our measures (in a SQL Server environment and perhaps other tooling): datawarehouse, cubes and reports. Where do you store your metrics? I've learned that storing metrics in the datawarehouse is the best option because the metric is available for every cube and report (generality) but i's also more difficult and costs more effort to build it in a datwarehouse than, for instance, in reports.
On the other hand when you build all of your metircs in the reports it's more difficult (if not impossible) to reuse the metrics in other reports (specificity). Building metrics in your reports is a less desirable option. So the next less bad option of building metrics in your BI solution should be in the cubes. It's more reusable than reports but lesser than a datawarehouse.
But still the best option remains the datawarehouse. If that's impossible/difficult try the cubes and if all other options fails, build it in the reports.