I've found that there are really no issues with regards to running a new OS for long periods of time. There was a time when regular reinstalls were a part of my regimen but that is long past. I reinstall only when there's a specific need. That doesn't mean I just put up with a slow computer either, I demand very fast performance from my systems. A reinstall just isn't needed to maintain that.
Likewise, components have gotten much better, and upgrades more incremental, so I've found the need to buy new hardware that would necessitate a reinstall to be less.
My guess? This person either has crap on their system that causes issues, or this is just a "magic incantation" they've always done for supposedly better performance without understanding or examination.