It's understood nobody "needs" the latest OS. However, there are risks involved in running older OS.
From Tom's Guide:
In late March 2017, per Google's own figures, Nougat was running on 3 percent of Android devices and Marshmallow had a 31 percent market share. But the other two-thirds of Android devices worldwide were running older versions that were no longer getting security updates. Those phones, hundreds of millions of them, were and are inherently unsafe to use.
--So, while you don't "need" the latest and greatest OS, you are risking security by not having a newer OS making a phone running an older OS much less safe to use.