1. They are extremely proprietary in nature. If your computer power supply ever dies, you will not be able to replace it with an off the shelf replacement. You will have to go through Dell in order to get one and then you’re going to have remove all of the innards of the computer just to get the power supply out and then in again!
2. If you buy a Dell Desktop, make sure to buy the extended warranty! It’s better safe than sorry! If you’re going to drop $5k on a massive desktop, what’s an extra $3-500 for the extended 3-5 years worth of warranty? I had a client who bought a massive $5k machine only to have the power supply go out almost one year exactly after purchasing it.
3. THEY ARE PROPRIETARY! I hate PROPRIETARY! You do not want to hassle yourself with this type of machine. If you do have to buy one or if you get one as a gift, I highly suggest, if your machine breaks, to take all of the components that can be taken out and place them into a new case with a new motherboard and power supply. The rest of the stuff should fit right in with the new motherboard + power supply.
To avoid any of this, just go custom and forget about buying a pre-made extremely heavy duty gaming machine. You will regret it in the end, I promise you this. I would NEVER recommend a Dell or HP or any other proprietary manufacturer for a gaming machine, ever.