For those of us who wish to enjoy the character of the places we visit without having to deal with crowds of like-minded people, traveling in winter is a good idea. Places like Paris, London, and Rome are less crowded in winter and travelers can take in the sights at a much more leisurely pace.
Of course, you may not be able to spend leisurely hours in cafeterias, take walks in parks, or hunt for bargains in summer bazaars but you will get the most out of your visits to art galleries, museums, cultural events and such places. In the summer-time these places are too crowded but if you are an art lover then a visit to the museums of Rome, London, and Paris becomes immensely more pleasurable when you have time on your hands.
The Vatican museums are far too crowded during the summer for one to really take in the grandeur of the works of the great masters. However, in winters you do not have to face queues extending up to 300 yards and you are free to gaze for hours if you wish at the ceiling of the Sistine chapel or visit the Colosseum and imagine what it must have been like during its heyday.
Luck is also a factor because you may have to put up with the occasional winter shower. Yet, inclement weather allows you to see features of a place in a different perspective, stripped of the multitudes; the plazas and squares present a different look. The restaurants catering mainly to locals put on display flavors different from what they serve to tourists.
Not to forget, prices in the off-season are significantly lower than what they are in peak season.