So, I'm currently editing a few songs I recorded - When I add effects to a track such as "Full Reverb", it gets marked out in a red color and I can't edit the settings of the effect while the song is playing - which I find very inhibiting, since it's nice to hear what you are changing and tinkering with as you do so. (Not to mention it's easier to figure out what settings do that way)
Full reverb is extremely processor-intensive, and to work at all it has to pre-calculate what it's going to do with your signals. If it didn't do this, you wouldn't hear it at all. And as a consequence, you have to wait for it. Not only that, but if you alter any of the parameters, you have to wait for it to recalculate. If you want to hear immediate results, with very little reduction in quality, use the Studio Reverb.