The Due to a screen fade issue with my Samsung S7 I recently had the chance to downgrade temporarily to my old Samsung S3.
The first thing that I noticed was how much smaller the old device is, both in terms of the physical device and screen real estate. Welcome to zooming and scrolling! From a development point of view it is all too easy to think of these two devices as the same format but that could be a mistake. It may be good to consider making the main view different for small handsets.
The second thing to hit me which was more profound was the performance, or lack of. I removed every app I didn't absolutely need. It turns out that still wasn't enough. If you are wondering why your older remain relatives or friends are so slow to message back; this is probably why. It is so tempting, as a developer using the latest handset, to think people will upgrade their handsets. Guess again, according to the official Google developer pages a massive 36.3% of android handsets are running KitKat L19 or lower as of January 2017. If you are building a mass market app this simply isn't a demographic that you can afford to ignore.
There are some tech companies who occasionally do downgrade testing for a large set of their employees. Facebook is one noteworthy example.
Many apps just can't run in usable time, by that I mean that they remind me of using a x286 without the Coprocessor. A particularly bad example was the twitter app which crashed every time that the "share content on social" hook was called to find contextual information.
The question remains, does developing for the latest hardware first make sense if you are trying to reach mass appeal or does making your developers start with the end in mind ensure your app will succeed?