This got way more interesting
So many players are pointing out some fundamental problems with practicing war attacks in standard multiplayer.
1) Bases you are facing are not optimized for defense
-Typical multi-player bases aren't going to have storages in the outside layers and may be better set up to defend against Barch and Giant/Archer than your big nasty war combos
2) CC troops are not optimized
-Facing off against 1 witch, 2 wiz and 1 loon - all maxed - is a WHOLE different game than 30 archers
3) Hard to find a comparable layout to target base
-for the above reasons, but also you aren't likely to want to throw a war army at a base with no loot... conflict of interests (loot or a challenge)
But I say its worth practicing war attacks in multiplayer for a few reasons.
1) If the only time you use a troop combination is in war, its going to take you a long time to get comfortable with it
-you only average 1 attack a day! Kinda hard to learn anything new then
2) You can still learn the nuances of troop AI and behavior. Figure out basic problems and possible solutions.
3) Its like a warm up, helps prepare you verses cold turkey
I don't always practice, but if I have a new troop combination or feel rusty I will. I also do it if I feel like I am stretching to get the 3 star on a particular base. Sure its not the same but I perform better if I get a little practice in anyway.
EDIT: But keep in mind I war with the following
GoViz
GoVaPe
GoWiVa
HoVa Variations (make specific to base)
VaLo Variations (make specific to base)
Quad Viz
I sometimes get rusty with one of the above and need a refresher. Also at Th10, I always practice. Very little forgiveness at that level for mistakes