This simple Military Policy lets you build the most 'military' district and its buildings more efficiently. However, depending on how many Military Policy slots you have available in your government, it may not be worth your while - 30% boost isn't such a big deal, and unless you're constructing Encampments and/or buildings in them in multiple cities, then there are other Policy cards which are more useful (such as Conscription). But if you have more than 1 slot, and no pressing concerns, Veterancy will speed up these constructions.