Logistic Units are for logistics handling, not for selling purposes. Logistic units can be packed hierarchically, so you don't need a direct relation between units and pallets. But if you want to sell in different packages, you have to define different UoMs, such as unit, box and also pallet, if you are selling complete pallets, each of them based on the UoM unit.

This question has also puzzled me for a long time. Ultimately you are free to interpret the three fields "The number of packages by layer" (ul_qty), "Pallet Logistic Unit" (ul_container "') and "Number of Layers" (rows) as you like because they are not used anywhere else in the system (the terms between brackets are attribute names in the code). To me, the most sensible would be that they refer to the type of packages of the level immediately below in the packaging hierarchy, rather than to of a type a level up, as the data filled in should say something about this packaging configuration rather than some next level. So ul_qty is the number of packages of the configuration of the level immediately below that fit in a layer within this packaging configuration, ul_container (a better name would then be "ul_contained") is the logistic unit of those contained packages and rows is how many layers of those packages go in this packaging configuration.

By the way, the fields are dropped in Odoo 9.0 so this is only applicable to Odoo 8 and below.