Question

Certain vehicles can be started by keeping the gears engaged, while certain others cannot be - explain?

Answer 1

Not certain I can give a profound, engineering clarification yet I realize that Automatic transmissions require that the move is in the park before the starter can be introduced.

Standard transmission vehicles can be begun USING the gear. Hold the clutch, get pushing it, pop the grasp while the vehicle is in first gear and this will turn the engine. This can begin a motor for a vehicle with standard transmission. For when your battery or starter is on the fritz.

Petrol and diesel engines as a rule have a grip which is utilized to associate the drivetrain to the motor, these vehicles can't be started without utilizing the grasp to detach the drive before starting.