Full manual and a pre-planned measurement trial and error is all good, but completely useless for a mobile setup where you cannot control every aspect of the lighting.
Utilizing a setup capable of TTL can still allow you to control the lighting via ratios without worrying about exposure as much. Yeah, all of you are so awesome when it comes to a studio setup where once you have everything measured out it never moves, but that is completely useless when it comes to a often-changed setup inside, outside, morning, sunny, beach, snow, etc. Digital gives you the flexibility of trial-and-error on the spot, but that is not capable with film.
I can either setup everything and take light measurements for the next 20 minutes, which are pointless if the outside ambient light changes. Using a setup capable of TTL speedlights allows me more control than any setup you guys are offering.