Two minor points:

1. Efficient (elegant) code and understandable (well-documented) code are not diametric opposites. Building in efficiency when the code is first written need not add substantially to the cost. Optimising existing code at a later stage is a different matter.

2. The need for optimisation of memory use and CPU cycles has gone. The focus now is on optimisation of comms capacity. A web page that takes 5 seconds to load is likely to be useless. A client-server app that requires 40 separate TCP messages may perform well on a LAN and then die horribly as it is moved into a WAN environment.