Hi Aldo.
I think what they are trying to prevent is getting a habit to correct things in PS that should have been done correctly while taking the shot (something I'm more than occasionally guilty of myself); thus the advice to get the capture right first before attacking PS.
Exemples:
- framing the shot corerctly so as to prevent cropping as much as possible: cropping drops a lot of the pixels you paid good money for on the floor => potential loss of quality
- correcting exposition in PS: not possible for over exposure, noise increases fast when under exposing
- level horizons (my big problem, most of my shots need a correction...)
- white balance etc. are a bit less important to get right 'in-camera' but I find that starting from a correct setting makes the processing faster and more agreable
Anyway, unlearning bad habits is a lot slower than learning correct ones...
Sterkte
Remco