A Desktop CNC, specifically one with a Tool Changer, is an incredibly valuable tool for any engineer, designer, or product developer who needs parts quickly and wants to iterate. There is often confusion about what the value proposition is for this kind of machine, and how it varies from lower-cost CNC platforms. These are hardly platforms at all.
1: Mostly, you need a real CNC machine
This may be self-evident, but anyone developing any new physical thing needs to be able to create versions of said thing before producing it in quantity. A CNC machine mills these parts out of solid pieces of raw material. Do not confuse this with a 3D printer, a CNC router, or a DIY build-it-yourself CNC mill. They are not the same things! A CNC machine can cut aluminum (or stainless steel, or plastic...) exactly how you want it, without you worrying about poor surface finish or accuracy.
2: You should start with a Desktop CNC
A full Vertical Milling Center (VMC) is huge, expensive, and requires a good deal of attention. Crashes are expensive in both time and money when they do happen. Operating costs are expensive every day (lots of compressed air and electricity). Further, if you are a business, then someone needs to operate and maintain the VMC. This then takes the machine out of the hands of the engineer most familiar with the parts to be made. If the point is to enable fast design cycles, put a Desktop CNC with a Tool Changer (or any very-capable CNC) immediately next to the Engineer. This machine is safe and quiet to operate. It is user-friendly and intuitive. Finally, it does not require that facilities or operations get involved. This is what we call our One Person, One Computer, One Machine concept, and it allows development to progress quickly.
3: If you get a Desktop CNC, get one with a Tool Changer
First, the stupid reason: a tool changer (ATC) option signals that a CNC is heavy-duty. Nobody with sense puts an ATC on a CNC router (although people do it). A Desktop CNC with a Tool Changer is NOT a CNC router. Routers are great for thin sheet goods, CNC machines are true 3D milling centers.
Second, the real reason: you can't make many parts with 1 tool. Or even 2 or 3. HAAS VMCs offer a minimum of 10 or 20 tool positions. Some may question whether that many tool positions are necessary, but anyone who has programmed a couple complex parts on the one VMC machine would be clamoring for more. The Desktop CNC machine with a Tool Changer is no different - it offers all the same benefits of many tool options to the programmer. Plus it is way easier to operate for a layperson:
4: Multi-axis Workholding on CNC ATC Machines
This falls into the category of "reasons why you should get a Desktop CNC ATC Machine instead of a CNC Router." Routers perform what CAM programmers would call 2.5D operations. (A tool goes to a height, then does 2D operations. That height can change, thus the additional 0.5 dimension, but it generally isn't 3D contouring in real-time). True CNC machines use coordinated 3-axis motion, they are rigid in all these axes, and they usually offer additional axes and the Z travel to make use of them! Consider a modular 4th axis that is available on high-quality Desktop CNC machines. The module is straightforward to install and align and offers the operator and programmer (hopefully the same person) access to four sides of the stock (imagine a cube). For most parts, that's it - one setup, one program! Multi-axis workholding offers very clear benefits here.
Adding a 5th increases complexity to be sure. But for certain parts accessing a 5th side, or approaching the part from compound angles, is well worth the complexity. For example, here's simple part done in one setup:
5: A desktop CNC machine can be a stepping stone
One day you might find that you need to produce larger parts at higher throughput. That's great, because you already know a) what you are looking for in a larger machine and b) how to use a CNC machine with a tool changer. All the functionality is the same. A floor-mounted VMC is just a larger, faster Desktop CNC machine. Now you have two of them!
Also: training. Why put green operators and programmers on a dangerous and expensive VMC? Especially when programming 4- or 5-axis setups: run it on the machine that won't hurt itself or the operator. A crash on a Desktop CNC machine takes 10 minutes and $10 to full recovery. For this reason, many technical education programs use Desktop CNC machines as a educational tools.
Conclusion: A Desktop CNC machine with Tool Changer is an invaluable addition to any company developing a physical product. Whether you already have a machine shop or not, put a machine next to the engineer and watch how fast development progresses.