If you value a cup win over PL survival, sure - that makes sense. I don't.
Otherwise there is a) an equal chance of getting injured in cup / league games, so why risk key players in the cup (which we have limited so far), and b) the 2nd string have the same opportunity to prove themselves in the League cup, which is now meeting PL sides anyway, and c) if we will 'definitely' rest players at some point, make it the cup games.
A cup would be great, but it's a pretty slim chance and IMO shouldn't distract from getting points in the league. YMMV.