Why trigger a TTL external flash (ie. hvl-43am) with ugly onboard flash?

Doesn't this defeat the purpose or am I missing something? I have an A77 and it can trigger external flashes with the popup flash. That's great and all, but the whole reason to use external flashes is to AVOID using the straight-on flash to prevent redeye, etc.

I've heard someone say they just turn the flash down manually on the camera and that works to avoid the pitfalls of the onboard flash.

Also: can the A77 trigger multiple flashes or just one? I've heard conflicting statements about how many it can trigger. I've read that the F20AM is nice because it can "trigger multiple flashes instead of just one". Maybe different camera models have different capabilities, but it's rather confusing!

Thanks!

--
1500 years ago, everybody knew that the Earth was the center of the universe. 500 years ago, everybody knew that the Earth was flat. And 15 minutes ago, you knew that people were alone on this planet. Imagine what you'll know tomorrow. -MIB