Two sims can be also useful for traveling - while much less of an issue in EU now thanks to the mandatory free roaming, it is still valid for traveling outside of the EU, where it is generally much cheaper to get a local prepaid sim card for the duration your travels rather than to use roaming.

Also Japan is an interesting case - you will only get prepaid data sims as a tourist for some reason. So having the dual sim capability could be useful as you can use your "normal" sim for any calling/SMS and the local data sim for data.

(For the record: Sailfish OS on the Jolla C had some serious issues with the Japanese prepaid data-only sims during our trip in summer 2017. The connection was unstable and even if it was working Android apps would still think they are offline. In the end I solved that by buying a used unlocked Android phone for ~7000 yen in Osana and used it as a WiFi hotspot with the data sim.)