My question is simple: what is Time.deltaTime, and why would we use it?
It’s the time passed since the last updated frame expressed in seconds. It’s used to move things with a constant velocity for example and is crucial for timers, animations and such. Because frames ain’t fixed-timestep (meaning one frame maybe take 0.1 seconds to process when another frame maybe take 0.2 seconds to process), we need to take this time into consideration or game speed would be different on diffrent machines. On a super computer, your character would be running 10000 mph where on a slow computer your character might be running in 1 mph.
If you multiply movement with the delta time, then you are compensating for this difference, and produce a smooth animation.