Overscan, H/V position, H phase

Hi,
I have been reading the FAQs and other sources but have not found a good yet simple explanation of these terms.
In particular, on my Hitachi TX100, I have found that H and V position is very convenient to shift the picture small distances (the lens shift is too coarse). Am I compromising anything else when I do this?
What actually happens - is the image moved to an unused part of the LCD panel?

Also, I see Overscan resizes the image. What might I be compromising and what actually happens inside?

H Phase does not seem to have any effect on what I see.

I would be grateful for links to good info or direct answers.
Thank you