Starbases are not new to the Rebellion expansion for Sins of a Solar Empire and not part of the original, having been introduced in one of the DLC packs that were launched during 2010 by ironclad Games, but they are part of the core strategy of the game.
Sins is a very fluid game and turtling seems hard to pull off and a losing strategy in the long term, but the new technology victory introduced in Rebellion makes it easier for defensive-minded players to actually win the game.
Starbases help very much in this regard, mainly because they can be customized in a number of ways.
Of course, there are the various options to add more plating, more shields and more weapons to keep enemies at bay, with a number of technologies for all the six factions allowing for even more defensive power to be amassed.
But a starbase on its own is nothing more than a speedbump to a determined enemy who knows how to move around the systems and how to employ his special abilities, as I quickly found out via the painful means of defeat.
The key is to pair starbases with slimmed-down fleets and make sure to move around quickly and also use plenty of repair platforms and turrets.
This only makes sense if you are under heavy assault from more than one enemy player, especially when dealing with humans, or if you are aiming for the technological victory that lies at the end of the civilian tree (which costs quite a few resources).
Also be sure to boost the massive starbase with other defensive structures, especially the jump inhibitors and the hangars that offer more strike craft.
All credit goes to the ironclad Games developers for the fact that, despite their introduction, Sins of a Solar Empire manages to remain a fluid and quick experience that never devolves into space trench warfare.