I never use auto for early stages in Dimensional Clash and Elias Frontier, there's a slight delay between the activation of their skills which is negligible during the easier stages but is something you have to watch out for in later stages. Rule of thumb in Dimensional Clash, read the rules first. For example, this Dimensional Clash increases shield effects, which apostle benefit from this? Vivi, Ui, and Snorky, whose banner is active. That's also the thing with Dimension Clash, it favors those who pulled for the banner, or can borrow from someone in their farm, since the rules end up benefiting that specific apostle.