A good follow-up to this would be, given all the externalization potential, what aspects of cognition should we aim to internalize?

Couple of offhand thoughts for this:

I do not mind the externalization, as long as it's sufficiently reliable and I can function without my iPhone in the worst case. (there is a great description of this in Accelerando when Manfred's augmentation gear gets stolen; in short it takes him a while to figure our who he is). This is the practical/operational aspect.

The other part of externalization that concerns me is that it makes me prone to the equivalent to looking up the answer key without having to work through the problem mentally and improving my thinking algorithms.