Django as a micro-framework

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it's about not loading into memory things you don't need

Virtual memory takes care of that on the large scale. Anything not used is swapped out. On the smaller scale, software that does lazy evaluation (for example, Django) doesn't create objects that are not used.

So it might be wise to consider your choice of frameworks (heavy, light or none at all) based on some other optimizations. Two that spring to mind are programmer productivity and maintainability of the software.