- Being able to detect noise from the system clock crystal oscillator all cross the breadboard (using my oscilloscope)
- Seeing certain I/O pins float to a bit too high of a voltage, when they were supposed to be "low", probably due to breadboard capacitance
- Accidentally making an AM radio when I forgot to connect a wire on an LM386 I was testing as an audio amplifier
Things got a lot cleaner when I went to a PCB, but I did make it all work on breadboards first.
And thanks :)
Cardboard is a fantastic material. You can draw the schematic on, and then run copper tape along the schematic. It's easy to annotate, since you just need to use a pen. It's able to handle much more current than a breadboard, since the copper tape has a lot more metal than thin wires. You can solder directly to it, and with tape (or some other insulating material) you can cross wires without having them short.
You can also work with SMT ICs. Using a pair of scissors, you can make your own pads and solder to them. I connected an SO8 to read off the SPI data using copper tape. I built an amplifier using a spare Novena amplifier IC on cardboard with copper tape. And I have a level shifter done on cardboard with copper tape.
Bunnie has a good article on it here, including an example power regulator that's handling 2A on cardboard: https://www.bunniestudios.com/blog/?p=5259
(It seems like it's still a thing in fact http://www.nutsvolts.com/magazine/article/wire_wrap_is_alive...)
It's a really nice way to work, you solder your components onto one of those pcbs with a lot of holes, solder the pins next to em, and from that point on you can wire, unwire, and rewire to your hearts content. Its great to easily be able to undo a connection when you make a mistake.
However, I’m not sure if there is an easier way to get quickly prototype electronics. Opting for more ICs and a lower BoM count helps, because there’s less wiring to do in the first place.