Depends a lot on the time. When it's work traffic a.k.a. rush hour, tram might be faster. Early in the morning or late in the evening, car is faster. But mainly I use it in certain situations, for example if you missed the last tram, or the tram can't drive because of a car blocking the tracks and you have a meeting etc.
It's just nice to have this "backup" besides public transportation, without the downsides of owning a car like maintenance, insurance, gas etc.