(Admins, feel free to move this to off-topic if necessary since I wasn’t sure where to post it)

So my house was built in 1978 and has 100A of total power available. Originally, I thought (from what the labels on the breaker panel said) that the second floor had a total of 45A available, with one breaker serving the two front bedrooms, one for the two bathrooms, and one for the back bedroom and extra room (that I now use as a guitar/music room, was an office originally). Actually, it turns out that only two breakers (30A) serve the second floor. The first breaker is connected to the outlets on exterior walls in the front bedrooms and the back bedroom, as well as the three outlets in the first bathroom, one out of the four outlets in the second bathroom, the fan and recessed lights in the second bathroom, and two out of the three outlets in the music/extra room. The second breaker is connected to the outlets on interior walls in the front bedrooms, the other two outlets in the back bathroom, the lights in the front bathroom, the last outlet in the music/extra room, and the fan in the front bathroom. I learned this after attempting to use two 11A window air conditioners on opposite sides of the house since I thought they’d be on different breakers, but this obviously tripped the 15A breaker very quickly. Is this setup normal or kind of random?
If that doesn’t seem weird enough my house also has 30A for the unfinished, unused, and basically inaccessible attic and 50A in the garage.

Most old houses has had dozens of patched in devices and other weird extensions of circuits. It makes finding breakers for things a pain in the butt and stuff can get overloaded quite easily. As a great example, my grandma's house that was built in the 1950s has a 100 amp panel. Most of the lights on the main floor and the basement are one one circuit, as well as a few outlets. The bathroom GFCI is run off the washing machine/furnace control circuit, a bunch of outlets tie into different circuits, the kitchen has 4! breakers for 6 outlets and the fridge. There are questionable ways of hooking thing sup all round, and crowded hell boxes and 70 year old cracking cloth romex. This is rather unfortunately quite common with older buildings and could only be reminded with a planned house rewire from every angle.

Its not unusual for houses to be wired based on what's the easiest place to run wires so long as there's adequate capacity in each space. My house is that way to a great extent. When I look at what each circuit powers, I can see now that the electricians just ran wires to each general area of the house and then fed whatever loads were in that area with the wire that ran that direction. For instance, half of my bathroom lights, the ceiling fan, one corner of the living room, and the kitchen range hood are all on the same circuit. Why? Because it was easy to run one wire to feed all of those loads that basically share one wall. That's not too much load for one breaker, so it all works out.

It would be nice if each room had one breaker for the receptacles and one breaker for the lights, but that would require extra wiring. Though the upside to this system is that the receptacles in each room are usually divided between two or more breakers, so tripping a breaker doesn't take out all of the receptacles in a single room. Instead, it takes out half the receptacles in two rooms.