Do you need a tour to see Florence- London - Rome?

There are so many great tour books out that you can plan your own tours and understand what you are looking at. In most of these places, sites are close together and when they are not the cabs are cheap. The only advantage is that the tour takes care of getting the tickets and you do not have to stand in line. However, read Rick Steves or Lonely Planet and they tell you how to get you own tickets in advance. The bad part of a tour is that you cannot linger if you want to, and if you are touring a gallery or museum all forty of you are in front of the same piece of art. Without a tour you can often have the area all to yourself. Will you miss something important? Maybe, but on the other hand you may encounter something unexpected that you would miss following the lady with the raised flag/umbrella.