My husband and I have taken a lot of pictures during our travels. During our southwest trip we took over 8,000 images. We had over 9,000 from our holy land trip and 5,000 from our Panama Canal cruise.
The largest card my husband uses is 8 GB and that is because his SLR takes 18 MB pictures. Most of the time I use a 2 GB card although I do have two 4 GB cards. When there are 8, 16 and 32 GB cards available, why do we use the smaller ones?
There are two simple answers and both we hope will never happen.
1) Card gets damaged.
The card can be damaged in several ways. If the camera battery power is low and the batteries poop out while an image is being saved to the card, the entire card could become unreadable. The card could be dropped or otherwise mishandled.
2) The camera and card get stolen
By using a smaller memory card less images will be lost if the card gets lost or stolen. Imagine if you used a 16 GB card for an entire trip, only to arrive home and found out that the card was not readable. As for it being stolen, I've heard of people telling the thief they can have the camera but please return the memory card.
My husband and I use memory card cases like the one shown below. The case holds the cards snugly and is water resistant. When we are out and about, we each have a card in our camera and a spare card in the simple plastic cases they come in.
At the end of the day, any full cards go into the memory card case while an empty card is removed from the case, ready for the next day.