Pressburg commands the Danube, on which Budapest also sits. This implies a couple things. First, if we assault Pressburg, we can use the fleet to help take it, and then use the same fleet to help take Budapest. If we do not assault Pressburg, the fleet is essentially out of the fight and we will not have it available to help take Budapest. Second, the Danube is the single best logistical artery in the area, surpassing Austrian railways in throughput and needing less [negligible] labor to make it usable. But only if we command its entire length. The assault on Budapest will be better-supplied, thus more likely to succeed, if we take Pressburg than if we bypass it.