Ive built a Lot of projects from Scratch, without so much as a quick pencil sketch.
For example, I built a complete working StarWars yoke, On-the-fly. No Cad. And only limited sketching at best.
Cut parts out, sanded them, drilled holes, cut shafts, mounted gears, routed and chiseled out the handles, etc...
Anything Innovative is going to take some work, and possibly a few revisions. But not everything can be done well in Cad... if you even know how to use it well.
For example, some people might design, or copy a design, that has a commonly reproduced flaw... such as a control panel that has no angle... or too steep an angle. Maybe they space the buttons out curved, but find they dont like the end result. Maybe the trackball ends up too close to the sticks or monitor... or the controls are too deep in the CP to be comfortable when playing for more than 5min spans.
Point being... is that you cant always get a good result, without some physical test, with some trial and error.
Ive failed on certain projects, such as a 6 way shifter... but I also learned a lot about the mechanics of the device, material worksmanship, martial stress factors, and much more. At that time, I couldnt afford a 6 way shifter. There were no commercial 6ways.
If money and time is more of a concern than getting something right the first cut... then sure. But to say that one should not Invent or Build something unique? Thats just going too far... and IMO, its Laughable to hear someone protest such a thing.
Decide, first, exactly what you're building and stick to it. Think it through. You should have built the cabinet in your mind a dozen times before you even pick up the first piece of wood you're going to cut
Thats assuming you even know what you want.. and that your mind will never change.
I found out after making some CPs, that I wanted real restricted 4ways... and Real Leafswitch buttons & Joysticks. These things only realized after playing some real classic machines such as Robotron, Galaga, and MsPacman. I used to be totally against anything Leaf, until I realized my misunderstanding of how to operate them properly.. as well as the benefits they attain in gameplay, over Micros.
Im fairly knowledgeable about this stuff, yet there were many things even I didnt know or realize at the time.
If you change your mind... you jusy rebuild the CP... or whatever else you have built.
Or... you could just sit there forever in contemplation... never actually building anything, because you are waiting for a 'perfect design', that someone else already built... which actually came from a visonary, and plenty of revisions.