Is it good to jump start the car when the battery is empty? The correct course of action depends on the reason for it being empty.
If the battery is good but you just forgot the lights on, and it has been empty only for a short duration of time (lead-acid batteries don't like extended deep discharge), then go ahead and jump start the car. That's the fastest way. Please note to use the portable vehicle jump starter correctly when jump start a car. You have to be careful when driving the car afterwards because if you accidentally misuse the clutch and cause the engine to stall, there's a risk you can't start it again. But with a little bit of care, you can drive it.
If the battery is empty because it is old and dying, do not jump start the car by a car battery charger jump starter or other charger devices! The problem is that when jump starting, it is actually the donor battery providing charge. When you disconnect the donor vehicle, the only good battery in the electrical system goes away. The dying old battery in the recipient car can't act as a buffer for the electrical system. The alternator can then produce voltage spikes, destroying expensive electronic equipment all around the car.
So with an old and dying battery, you can try to see whether charging will remedy the situation. You can charge it slowly with a battery charger or rapidly from a donor car with jump start leads, but in that case don't turn the recipient car engine on. Then check to see whether the old battery is able to start the engine with charger / jump start leads disconnected. If not, it's time to purchase a new battery. If it can start the engineby a car battery charger jump starterkeep an eye of the situation and estimate when you need the new battery, if you need it at all.
If you forgot the lights on, and then left the battery sit for a week or two not bothering to fix the situation, then the health of the battery is unknown -- on one hand, the battery was good before the event, but on the other hand, lead acid batteries don't like extended deep discharge. So it is possible the deep discharge has damaged the battery. It's always safer to charge and then try starting than to jump start.