The most significant difference is the level of help you receive as a rider. The pedal-assist function senses when the pedals are in motion and begins to work with you. On the other hand, throttle mode will get you going without pedaling, similar to a moped or scooter. Both provide a different riding experience, and what you choose will depend on how you use your bike, and how much control you want. You'll also need to check if bikes with a throttle are legal in your area.