+1
Rack mount is primarily about organization and accessibility when you have large amounts of devices and cabling. In a commercial situation, you have to be able to reconfig a device within hundreds of servers and cables quickly and without disturbing anything else.
But there are some major downsides at home:
1. Cost: Rack mount servers are just more expensive. Rack hardware is REALLY expensive. Just the rails alone to mount a rack server can be several hundred dollars.
2. Power: Rack equip is mostly redundant and high powered, and that means a lot of electricity. Do you really want a 42U WOPR in the basement that's costing $100+ a month on your electric bill.
3. Noise: Rack mount servers alone may contain over 10 cooling fans. In the data center, noise is not a concern, but as you lie on your pillow trying to go to sleep, do you want to be listening to a steady hum coming through your house framing?
4. Transport: Keeping things small and ultra low power means you can throw it all in a box and move when you need to. A 42U rack alone is several hundred lbs weight.