[FFmpeg-user] dv => mp4: deinterlace or not, and how?

[sean darcy]

I have an interlaced dv file. I'm transcoding it with x264 to mp4.

1. ffmpeg -i file.dv -an -vcodec libx264 -b <x> out.mp4

If I just leave it like that, is out.mp4 interlaced or progressive?

2. ffmpeg -i file.dv -an -vcodec libx264 -b <x> -deinterlace out.mp4

Here I assume out.mp4 is progressive. The ffmpeg documentation says:

"The alternative is to deinterlace the input stream with `-deinterlace', 
but deinterlacing introduces losses."

Is this still true?

Given this note about losses, am I right we should never deinterlace? 
Almost never? When is deinterlacing required/better?

3. ffmpeg -i file.dv -an -vcodec libx264 -b <x> -flags +ilme+ildct out.mp4

Here I assume out.mp4 is interlaced. How is this different from 1. 
above? Is it different?

The FAQ mentions +alt as a flag. When should this be added? Does it hurt 
to use it all the time?

sean