I feel the need to point out that the T3 science lab doesn't actually chance Sarnian's point, as to create it, you still need to be in supply, so thus you would only be able to "raid" planets near you, and not planets farther away. To get supply to those planets then, you have to capture loads of planets. To get the normal science labs to work on them, you need to blow them up. Either way, to get knowledge from a lot of planets, you need to blow up a lot of planets, and even more if you don't capture most of the ones you blow up.
This also changes depending on which map you play of course..... But as an example, if you are playing a Tree map, and there is nothing you want down one tree, you can't just leave it up, and raid all 5-8 planets for their knowledge, and then move on, leaving a chokepoint behind. If you want the knowledge from the chain, you have to capture at least every third planet in the chain. If you are doing that, you might as well capture the whole chain. So, thus, even with the T3 lab, it's not really letting you get very much extra knowledge. In my experience, just a planet here and a planet there. Thus, I almost never use them.
Which I guess goes with the "never use it unless you are stuck" comment, but that seems a little.... restricting....
Maybe the T3 lab could be made mobile? Make it so that it has to "deploy" before it can get knowledge, and takes a while to "pack up" so that it can be moved again. And during the deployment and packing up, it would be making the AI mad, and also not getting any knowledge. And, it would use full power the whole time, either mode. Think of Siege Tanks from Starcraft, now imagine no gun while in the mobile mode. Now apply to T3 science labs. :-)