They say there's nowt new in engineering!
Generally, the UK car-parc in the late 1950's / early '60's was Dynamo- equipped.....there was an anomaly, called the "Siba Dynastart" A complex ignition-switch enabled it to act, as stated by other posters, , as a motor and thus start the engine....releasing the key would change connections to the "generator" configuration and it would generate DC and charge the battery via an electro-mechanical regulator box,
The interesting feature was the ability of the switch to be operated to engage alternative contacts and ignition-points.....the engine could thus be run backwards! Anyone who drove a Messerschmitt KR200 3-wheeler with 4 reverse gears, can attest!it was good for 70MPH either direction!
Early motorcycle alternators were somewhat crude....the Rotor, direct on the crankshaft, was fitted with permanent magnets. the stator fed through a 3-phase rectifierand voltage controlwas via a Zener diode, which, at it's designated voltage, dumped surplus output into a heatsink.
Some modern Alternators still have a residual, low level magnetism in the Rotor, These will self-excite, the output being directed intothe rotor-winding to increase the magnetic field and therefore output. Surplus is switched to battery and acessories, via the regulator,which controls the field -current to regulate output.
On some designs, the initial Field-excitation is via the charge-light this is battery-fed and finds it's return via the Alty field (thus weakly magnetising it, as it's in series with the bulb) When the generator starts producing, the output opposes the battery voltage and current stops flowing .....so the light goes out!
other variants are governed by the regulator and there are also alternators with remote, electro-mechanical (coils and contacts A la doorbell! ) regulators.
You cannot use an alternator as a motor. that is the only disadvantage i can think of.
As the rotor just has a single coil, it'seasily balanced and mechanically robust....contacts are via slip-rings, which, having no segments, make for a lighter, longer-lived assembly.
the stator-windings ar actually in 3 SETS ! Thus they take advantage of both ends of the rotating-magnet's poles, to produce output. As they are static, there is little mechanical stressand , needing no iron casing means lighter weight and better cooling.
I have little knowledge of large-aircraft generators, but, as others have said, high voltage AC has less distribution-lossesand is readily altered via a transformer. Itcan then be rectified to DC if required.
AFAIK, turning DC to AC, via a solid-state Inverter, is less efficient.
In the early 60's there were "rotary convertors" offered by government-surplus dealers....these were essentially a motor and dynamo built into one unit...veryexpensive and very inefficient....but I suppose it's all relative when you are feeding four Merlins on full chat!