There are lots of considerations when using the Rapture. The first and most important (with any capital ship) is survival. Sometimes you just do not want to get too close to an enemy fleet with your capital ships, and in this case the Rapture can still contribute by empowering carriers. The second consideration is using Vertigo and Vengeance. Obviously if you're sitting far away from the enemy these abilities will not get used much, if at all. Thirdly, there's the matter of how many carriers we're actually talking. If we're talking about 2 or 3 carriers... not worth your time. If we're talking about 20 or 30, then you definitely want a Rapture standing by those carriers, so much so that it may be worthwhile to build a second one if you want to have a Rapture with your main fleet as well.
Anyways, a level 1 Rapture with concentration aura is really only worthwhile if you have about 25 drone hosts (75 squads). I'd definitely consider this a secondary ability, and use it primarily if I don't want to take risks with my prized Rapture, or if I have a huge number of drone hosts to buff up.
