You may have seen some higher-end air beds advertise the use of an integrated layer of memory foam to make them more comfortable. There are a number of customers who say it is redundant, because they can adjust the softness or firmness of their “premium” air beds. There are also customers who say their air beds are like balloons that de-form to fit their body-shape, so a memory foam topper actually makes the air mattress less comfortable.
However, I am currently sleeping on a cheap air mattress. I cannot easily adjust the firmness of my bed, unfortunately. Even more unfortunately, my air bed is not very balloon-like. If I pump too much air into it, it becomes quite firm. At these times, I definitely wish I still had my old memory foam topper to put on the air bed.