[inkista]

Most people do, especially in posed situations where you have the ability to adjust and retake. I find Manual/eTTL on flashes to be pretty analogous to the M/Av modes on the camera. M gives you total control via settings, Av gives you exposure compensation, but no idea of the metering algorithm being used.

eTTL is better for run'n'gun situations where you only have one chance to nail it (event photography), and has the added bonuses of giving you remote power control (i.e., you don't have to run about from flash to flash to adjust the power settings), high-speed sync (so you can shoot above your X-sync speed), and stroboscopic mode. But you do have to ride the FEC a lot, just as you use exposure compensation in Av mode.

It's nice to have both, but most folks find they can ditch eTTL pretty easily when they're playing with off-camera flash.