If combat provided absolutely nothing and only wasted time and resources, then it would be easy to argue that combat should be avoided if possible (unless you just wanted to fight because you find fighting fun).
That said, PoE combat provides items and crafting ingredients. There is clearly some incentive to fight, even if that incentive is not XP. From this perspective, combat should be avoided unless it provides a net increase in player resources (or is unavoidable).
A bit like real life. LOL! So for once I agree about a game decision. I think it is very intriguiging to not give xp for combat. It makes you rethink many of your choices that would otherwise be standard in a game of this type. It is a fresh perspective and I support it.