I lived in a city with a "trolley" that turned out to be a bus painted like a trolley and I've heard of others with the same experience. I have to laugh when I see a city advertise it's trolley service when in reality it is nothing of the sort.
I suspect the benefits are you don't have to lay rail + you can use normal vehicle lanes + you get the benefits of not having a combustion engine (smog, mechanical issues, fuel storage/re-fill).