This should be a fun topic, the power users are consuming must swing by magnitudes. I wonder what the largest energy demand anyone has for reasonably heating/cooling their space. There are probably some arctic circle EEs who would literally die if you took away their old scopes and meters. All those neon indicators and CRTs really warm the place up!
Having just gotten into electronics I've been working on things nomad style throughout the shop. I don't really have any equipment yet, but even looking at some of the more populated benches around here I can't imagine having enough desktop stuff to need more than a single breaker. Here my electrical concerns are mostly with outlet count. Those long strips with outlets every 200mm or something are perfect for running behind almost every bench or desk. For stacks and clusters of instruments gangs of 2-4 standard outlets are ideal (Ahh, phantom!). Usually the practical solution is to just plug in devices as you need then, since most people don't jump between dozens of devices on a daily/weekly basis, or "the leads don't reach". Even simultaneously running a fairly high wattage desktop PSU, CRO, 80W iron, computer, etc. should be fine, though maybe close, on a single breaker. Plenty of power for most home projects I can think of...
Unless you want to put it in a 125*C incubator to test x/T or something silly. Things like that are what push up the breaker count. I have a lot of 1.5-2kw equipment, but most of it doesn't get used simultaneously, and shares a single breaker that is separate from my bench and lighting circuit. I also have a single 20A breaker that runs to an outlet through about 6ft of 12gu that I plug the air compressor into. Compressors have a sadistic love for kicking in just as you're pushing through a knot of oak. This is also used as my general purpose dedicated outlet whenever I need one, so mostly for running yard tools
The soldering oven (first project, woo!) I'm working on is >2.4kW, so I'll be driving it off of the 240v split phase. I'm trying to think of other projects to take advantage of that wealth of power. Building one of those local on demand water heaters could be fun. My garage/ climate mix allows for no heating in the winter (though it'd be nice) and in the summer I just plug in a fan that has a couple meters of copper tube strapped to the front that I pump coolant through. <100W.
To what extent is isolating test equipment necessary to ensure it gets fairly clean AC in? Do internal filtering and FCC regulations pretty much take care of that? It's not a problem for PCs, and I haven't heard it come up.
Coldhardstatz (TL;DR):
Breaker 1: 120V 20A
-Lights ~120W
-Computer ~300W
-Audio/Video ~200W
-Battery Charge Station ~50W (in practice)
-Soldering Iron 35W
-PSU 300W
-Remainder over 4 desktop outlets.
Breaker 2: 120V 20A
-Various Power Tools
-Garage Door Opener
Breaker 3: 120V 20A
-Dedicated outlet, used as needed. (Air compressor by default)
Breaker 4: 120V + 120V 30A (What's the notation for this?)
-Reserved for Future Use