I don’t personally view that as a convenience but understand the sentiment. If my PSU died, or something similar, and I had to send my entire machine just to get it fixed, that translates into working downtime for me.

It’s nice to just have some spare parts or your old parts to swap into temporarily while you rma the dead part. Of course, this assumes that you can do a bit of hardware troubleshooting (which I admit isn’t something most laypeople can do).