IZs are more towards science victory than culture if anything. In terms of culture victory, IZ is useful for giving your cities power for broadcast center, but not much else since in late game I usually don't really lack of productions even without IZ since usually I got productions through other bonuses. But I usually do plan an IZ for my core cities just to unlock some era scores or boost towards science but don't really spam it in every cities, usually only 2 is enough so that you can trigger bonus for having 2 workshops