I have now read enough applied circuit diagrams that I believe I'm missing something that is obvious to those skilled in the art: Where an abstract diagram has a few components, a complete wiring diagram of the same circuit is absolutely littered with capacitors in the microfarad range.
(To do: Find and insert some example images here.)
I can sort of understand how these capacitors would smooth out voltage drops, (and I guess there are usually a few diodes to deal with voltage spikes)?
But how do engineers come up with these applied circuits? Are there unwritten rules they just know, like, "Yep, gotta put a microfarad on this side of a diode, that side of a transistor, and three of them in parallel by this sort of switch…"? Or do they wire up a prototype, start scoping every junction, and add them based on actual signal noise they observe? Or is more prophylactic, e.g., "I wouldn't want a lot of voltage noise here, so why not add some capacitance just to be sure?"
Best Answer
In my experience, bypass caps are required next to modules that can switch state,(flip-flops, memory, etc.). If you don't do it, your circuit very likely will experience erratic behavior, and even failure. This is a lesson I learned on my own when my designs were working erratically and were highly susceptible to electrical noise. After that, I paid more attention to, and followed the recommendations of the module designers.
Then there is the matter of the project schedule. Usually they want the circuit/design working "yesterday." So, you have to decide, do you want to spend time determining where you need bypass caps or making/improving your design? If you take the recommendations of others, then you don't have to spend time on that.
If you work for a large company, other people will verify and test your design - which is good. If not, then you will have to do it all yourself, leaving the user exposed to any mistakes you might have made. An example of this, that comes to mind, is the Hover-board. There is a major design flaw with it, which was not caught (or ignored), before releasing the design to production.
So, yes, learning from the mistakes and experience of others, is part of becoming a better designer yourself.