I think I have answered my own question while writing this. I have been having difficulty fading title clips in and out while placed over video tracks. The black of the title clip appears instantly and then the colour fades in, very odd. But thinking about it, fade from black, this sort of makes sense.
Video shows what I mean here:
Anyway, I guess the correct way to do this (which I just discovered while messing around) is to use the composite effect, not just to overlay the title clip over the video, but to key frame the opacity in and out, which produces the desired effect.
So I guess my question now is, is this how people do fading in and out for title clips? I have very little understanding of the transitions, and would love to learn more, is there anywhere to read up on all of this? The alpha channel operation for example, and what all the different transitions mean/do.