I have traveled to Europe and South America: on my own, with friends, and with tour groups. For me, the benefits of a tour group, in addition to those mentioned by Sayhello are:
- Variety of people to talk to. Even with a friend or two or family, I enjoy the variety of different people.
- Not having to compromise. When you travel with friends or family, someone is always compromising. Or you spend alot of time discussing (arguing) about where to eat, what you're going to do, etc... With a tour, you go with the flow and on your free time, everyone can do their own thing (alone or together!)
-No stress in navigating - whether it be driving (I can't tell you how many times my sister yelled at me that I was going to hit the curb when driving on the "wrong" side of the road in England & Scotland) or navigating trains, buses, subways, or local flights.
- As Sayhello said, it reduces the stress of the planner, who is normally me (although you also lose some "control" too)
- Tour guides with you a good part of the day, so you don't end up hearing the same things over and over, and most all of the day is in learning mode.
All that said, there's something to be said for the spontenaity that you can have while not traveling with a tour group and all those unplanned experiences. If you're the type of person (and you are traveling with the right type of people) who can go with the flow and really relish those experiences (vs be stressed out), you can have a great time.
I actually prefer NOT to take
ABD trips with friends - I really enjoy my daughter and I having the benefits of a guided tour (I can turn off the "Mommy button"), while still having some freedom to spend time with different people on the tour or on our own. When you travel with friends, I think there can often be the pressure to do things together.