Kyuubi4269 posted...
It's like in school being made to memorise the periodic table like it isn't literally a lookup table.
It is a lookup table, but a lot of the more practical things you're looking up are worth memorizing to be able to use that information without needing to dig out a table every time. Specifically, column numbers (for non-transition metals) dictate a lot of the chemistry each element can be involved in, and knowing how each element relates to others is handy to relate to the various trends of reactivity, steric hindrance, and other properties that the periodic table indicates.
Of course, in practice, most people only use a small handful of elements and just end up memorizing the properties for those ones, looking up less familiar ones whenever they come up. Still, being able to skip a lookup step is handy, so it can be worthwhile to have at least a working knowledge of the table memorized, much like it's worthwhile to be able to do simple math mentally instead of having to fish out a calculator to double a recipe or whatever.