An oscilloscope displays voltage versus time. That makes it the ideal tool for crank and cam waveforms, wheel-speed signals, injector current ramps, communication networks and intermittent glitches too fast for a multimeter or slow scan tool.
You do not need an oscilloscope for every sensor fault. Many problems can be solved with scan data and a meter. The scope becomes valuable when you need to prove signal quality, timing or a very brief dropout. It can also prevent unnecessary parts replacement when a sensor produces the correct waveform but the ECU is not receiving it because of a wiring problem.
Scope testing requires care. Choose the correct voltage range, time base and ground reference. Be cautious around ignition secondary voltage, hybrid/high-voltage systems and circuits where the measuring instrument could create a short. Follow equipment and vehicle service information.
A useful learning strategy is to capture known-good waveforms on a healthy vehicle and compare them later. Pattern recognition becomes much easier when you have a baseline.