-- the pockets are loaded, probably not with handerkechiefs
-- if the person has a load on him, and he does not get rid of it,
the implication is that the load has some value!
It is a kind of 'imaginary' use of a term, not really metaphorical, but once it has settled, the original depicted scene is forgotten and the term (loaded)
acquires a new meaning.
Moreover, a load can be easily divided among people, so the 'value' is not anything moral or related to knowledge (those are difficult to share or distribute even by a willing person), but must be related to possessions.