We booked this in advance for our first full day in Venice. We wanted a tour to kick-start our visit and show us around. We loved the walking tour, but skip the gondola and do that on your own.
After the walking tour came the gondola tour. We got put to the side with other travellers while the tour organizers checked in a hundred or so extra visitors. We just stood around rather bored. Then, we were led to the gondolas, but the new customers got to go first. So, we waited some more whilst those guys got on the gondolas first. I know, I'm whining, but it was irritating.
Our gondolier told us, when asked, that he's been doing this for 25 years. I suspected he was a tad burned out. One of our party rested a foot on the side of a seat (polished wood) and got a lecture -- okay, I get it, but there was no scuff, no mark, and there are better ways to handle that. Also, the gondolier spent the entire trip talking to other gondoliers we passed or followed and really ignored us. Additionally, all the gondolas of a hundred people followed each other in a loop. I mean, riding gondolas is very quaint and a must-do for a first trip to venice, but we came to refer to this as our "Disney ride." The canals are unique and quaint, and don't smell in March, and the architecture is fantastic, and clearly the sea is rising and the buildings are sinking. We loved the canals. But this gondola ride was just not for us. And, then, the Disney ride ended.
So, we'd book a walking tour, we loved that, but skip a pre-booked gondola tour.
However, the next day we booked our own gondola ride. It was quite different. We actually wanted the gondola to take us to a particular wine bar, which he would do for 120 Euros. But, for 80, he would take us in a much longer loop (I don't understand this, even today), so we did that. This wasn't a train of gondolas all following each other. And, the gondolier spoke to us and chatted about some of the things around us. It was a much better experience. So, apparently, you can't really book a gondola to take you to a specific place, as one would a taxi, but if you want a gondola ride, and you should your first time in Venice, the best way to do it is to walk up to a stand, chat with the gondoliers, and rent a gondola ride ad-hoc right there and not as part of a pre-booked anything.