If it's infrequently accessed data then yes, but for a machine that you use every day it's nice if things keep working after a failure and you only need to plug in a replacement disk. I use the same machine for data storage and for home automation for example.

The third copy is in the cloud, write/append only. More work and bandwidth cost to restore, but it protects against malware or fire. So it's for a different (unlikely) scenario.