Packing lightly is definitely advisable for anyone who is traveling to a number of cities. Lugging a big suitcase from place to place gets to be a burden, and if you are traveling by train in Europe, there is limited space for luggage. At airports it is also nice not to have to wait around for checked suitcases to be unloaded.
However when I travel to Mexico I take my big suitcase.
Generally on those trips I am just going to one or two cities, so constantly moving around with a bunch of luggage is a not major issue. Besides, I am usually bringing some gifts for my friend Alejandro and his family, and I also do some souvenir shopping for myself and others while I am down there. When I travel to Yucatan and Mexico City, I need to pack two different wardrobes... one for the tropical climate of the Yucatan and one for the much cooler weather in high altitude Mexico City.
Packing for my trip to Switzerland and Norway next month is a bit more problematic. Since I will be visiting a number of different places, I don't want to be burdened with the big suitcase, but I am not sure that two carry-ons will be sufficient. Even in August, temperatures in Norway, especially at night, can be rather chilly. I need to take a warm sweater, which takes up a bit of of room. I won't be doing a lot of souvenir shopping (Switzerland and Norway are very expensive), but I do need to buy some gifts for a number of friends. And, from past experience, my Swiss cousins will probably give me some presents.
My strategy at this point is to take three pieces of luggage. All of them are of carry-on size, but I will check the largest of the three on my flights.
The backpack with the Swiss flag was a gift from my cousin Brigitta on my last trip to Switzerland. It is perfect for packing my mini-computer and some other small items. In the small red bag I will put my dress shoes and some clothing. In the gray roller-bag I will pack the gifts for my cousins, my sweater and more clothes. That is my plan. Perhaps when I start packing, I will find that two pieces will be enough. That would be ideal.