Although it's rarely called to be used in pentests I've done, it has, on occasion. That said, I think they put a lot of emphasis on it, at least, in the CSWAE, as well as the CEH class of old. (v7 didn't really touch on it much, IMHO, but my original CEH did.) Perhaps the older CEH materials are where they gleaned the necessity to hammer it in...
While yes, it is sometimes necessary to maintain access / cover tracks, etc, and you do have to understand it to be able to 'warn about it', rarely has it been something I've had to actually DO, in a pentest. (However, if you ever participated in the Cyber Challenge SANS did, etc, if you didn't do all the above, you wouldn't score well, as they regularly sniped participants, so you needed a fast and reliable way back in.)
BTW, from what I've had time to look at in CSWAE, I'm in agreement about the rest of the material, too. Granted, it's aimed more for developers, but ungh...
~ hayabusa ~
"All men can see these tactics whereby I conquer,
but what none can see is the strategy out of which victory is evolved."
- Sun Tzu, 'The Art of War'
OSCE, OSCP (Former - GPEN, C|EH - both expiring / expired)