I call these furdowns. I guess that is another regional thing.
Anyway, I have them also and feel that they are a waste of space. I investigated the issue and found that they were being used as a raceway for electrical wiring and HVAC venting tracks.
Now, not all are used in this manner, depends on the builder. If not used, then you can open them up and ceiling out the area and then insulate the above and use them for higher cabinets or whatever. They are a waste of space when not used for electrics.