I wonder how often it would ever get used. I can think of two times where I used a scope to troubleshoot a vehicle problem. Most electrical problems I've solved with a basic DMM.
Scopes can be very useful for
a lot of automotive diagnosis work, it's absolutely not limited to electrical.
We've been looking at ignition waveforms since probably the 1950s, it can find a bunch of issues in the ignition system (obviously), but less obvious it can point towards leaking valves (the flow inside the combustion chamber towards the leak upsets the spark), a cylinder running lean (partially clogged or non working fuel injector), cylinder running rich (injector stuck open), low compression issues (lower voltage spark required, with increased spark duration as a result compared to other cylinders) and so on - and that's just some information we can get from hooking the scope to the ignition system.
If we look at battery voltage during cranking (or current if we have a suitable probe) with fuel/ignition disabled so the engine can't start we can see the fluctuations in voltage/current due to the varying load on the starter as each cylinder is on the compression stroke, if the compression is not the same in all cylinder we instantly see one cylinder pulling less current - we have detected a low compression issue in about a minute, just removing the spark plugs for a conventional compression test takes far more time, and if it's one of those horrible modern cars that requires a lot of disassembly to access all spark plugs this may save hours - we still need to perform more tests to figure out why the compression is down, but we have gone a long way in a short time narrowing down where we need to look for problems. Add a sync signal to (for example) cylinder number one and you can figure out exactly which one has the problem.
The battery voltage/current while cranking can also detect a starter about to fail due to worn brushes, as the brushes loose contact intermittently the current will pulsate horribly. A worn fuel pump behaves similarly, but there you really need a suitable current probe to see it.
A bad diode in the alternator will cause a lot of ripple that may interfere with sensor signals, causing strange issues hard to diagnose with other tools - the alternator may still charge to the correct voltage, so hard to detect with a multimeter.
A simple, cheap pressure pulse sensor made out of a piezo speaker (pulled from basically any electronic device that beeps) lets you look at pressure pulses. Connect to intake and you may see if one cylinder doesn't draw in air (failed lifter not opening valve for example), one cylinder pushes air back into intake (leaking valve for example), similar possibilities with the sensor in the exhaust, put it where the dipstick goes and you see pressure due to leakage past a piston, connect to the cooling system and you see pressure pulses in the cooling system from a bad head gasket...
Just a handful of examples, the possibilities are really endless.