No offence meant, but am I the only one who thinks TTL is over-rated?
I'd suggest a consistent method over either of the two is most effective ... if you get used to TTL and understand what the camera is going to tell the flash, then you will work well with it. Similarly, if you'd rather not bother with that, you have an equally effective option of being able to test, adjust in manual too. Imho, it's a little like metering - use one method consistently enough and you'll begin to understand what all those chips inside you paid so much for are up to and you'll learn how to read them.
I agree. But, from what I have seen, a lot of people want to go TTL only because lighting manually (without the assistance of TTL) is a bit difficult concept to grasp, especially the ratios. IMHO TTL is over-rated because of the price you pay for it. Like Soam suggested, if I need to get 4 PWs, I'd spend a fortune. The other option is to get a TTL cord, which is quite limiting. Instead, I find it easier (and cheaper) to use off camera flashes manually and not rely on TTL. Yes, it does involve a bit of "chimping", but I guess most of us are okay with it or can be prepared in advance.
For on camera flash but bouncing the light off a wall/ceiling, TTL works much faster and easier to use. I think in such scenarios, it's totally worth it.