What MODULEs are needed and when?

[KerbMav]

Some parts do have some modules/parameters, others do not - when are they really needed, what do they do that some parts require them and some seemingly can go without them?

Mainly asking about these two for now, but I am sure there are more?

DRAG_CUBE

ModuleCoreHeat

[Starman4308]

I'm pretty sure the drag cube has something to do with stock aerodynamics. Core heat is for parts that produce heat during operation, such as drills and ISRU units. It basically manages the thermal inertia and heat transfer properties of the part.

Generally speaking, parts have only those modules they need.

[Red Iron Crown]

The drag cube module is for manually defining a drag cube for a part when the default calculation of one based on the part model is inadequate. Usually this is done for hollow parts like cargo bays. 

The core heat module activates another layer to the thermal module for a part, only used in stock for the isru parts. 

[Kerbital]

Here is module wiki. Although, I have not found the two OP asked about

http://wiki.kerbalspaceprogram.com/wiki/Module

Edited July 2, 2017 by Kerbital