I should have been more careful. Although people may favor one way when dealing with particular situations, everyone uses both mapping and packing learning strategies. Mapping is an attempt to understand. Packing is an attempt to memorize. Both ways help you remember.
When you need to remember someone's name, phone number, or birth date, a packing strategy may be appropriate. Unless you have some deep understanding of how these things work, this information is pretty much arbitrary.
This is the fundamental difference. It seems, we have little choice regarding information that seems arbitrary or nonsensical than to "pack" it in your mind. With information that makes sense, mapping out how the new information you come across makes sense, is very effective. For instance, when you learn the periodic trends after you know that oppositely charged bodies attract and that the more charge bodies have, the more they attract, it is really easy to remember that atomic radii decrease as you go across the period (it is a simple consequence of what you already know).
However, people have come up with "artificial mapping" strategies to aid packing. Mnemonic devices, and the tricks that people use in the Memory Olympics and such. These strategies don't map knowledge to new knowledge but rather, nonsense to other things (which may seem like nonsense). It is still relatively effective because the nonsense becomes familiar to those who use it. This involves things like: "SOHCAHTOA", "ROY G. BIV", and "My Very Energetic Mother Just Served Us Nine Pizzas."
But this is the reason I say that those who learn to "not look stupid" or to "impress people" will tend to favor packing over mapping.
Mapping is a personal and idiosyncratic process. It grows from what you know outwards towards what you want to know. It builds-up. It works from thing we understand to things we want to understand. Once you learn something this way, it is difficult to "forget" it. The new knowledge becomes incorporated and built upon.
Packing is just a means to some other ends. Once those ends are achieved, there is no longer any reason to hold on the means.