When a Pocket Dimension is created, spaces folds in and over itself wildly. Imperfections in this folding allow for the passage in and out of these pocket dimensions. Such openings are etheric gates. It is theoretically possible to have a pocket dimension so dense that it folds perfectly and creates no gates, but this has yet to ever be documented.
Etheric gates allow access to the cosmos, but the bottleneck nature of these gates and their attached hyperlanes(ley lines?[CONFIRM]) makes them prized possessions on any planet which has discovered them. This has far-reaching impact on many aspects of societies inside Pocket Dimensions.
As there is no other remotely safe way to traverse between The Aether and pocket dimensions, cities near these gates naturally become local trade hubs, and planets (like Aeldrum) which have many gates become natural cosmic trading centers. Having many gates not only allows for a larger flow into and out of the planet, but also typically connect to other worlds much more easily as the gates are usually located on Ley Lines. Ley lines move slowly over time, so not every etheric gate is connected to ley lines, but they are usually still in close proximity.
Worlds with a medium number of gates can serve as barracks of sorts for troops. When a large number of troops needs to be deployed, it is better to have several gates to increase flow off-planet. Too many gates is undesirable as it makes the world more difficult to defend. Though this is not a problem for prosperous worlds like Aeldrum as they can finance the larger military force needed to maintain coverage.
Several conundrums common to sci-fi universes disappear as a result of the Aether and etheric gates. First, planetary bombardment is impossible to effectively conduct through the folds of the Aether which surround a planet, making it almost impossible for ground troops to become obsolete, as they tend to logically become in most "ordinary" universes (especially after the development of atomic weaponry).
Second, new planets may be introduced at any time, in any location in the planetary network, as etheric shifts and further research cause new etheric gates to be discovered. Third, the Aether restricts the movement of people and stuff, which both makes for interesting strategic choices, and for fewer silly arguments about how someone should have "just gone around the place".