Questions on water to grist ratios

Let me start off by saying I haven't brew all grain yet so this may be a basic question.

How does the amount of water to grist ratio affect the mashing process and final product? I've read that "normal" ratios are anywhere between 1.00 quarts/lb up to 2.00 quarts/lb. Why would one choose one over the other? Do different sparging strategies require different ratios?

I've heard that for beers that allow imperfections to show much easier (i.e. pilsners) that it's better to use a higher grist/water ratio and sparge with less water to reduce the risk of extracting tannins, etc.

I personally like to mash a little thicker for higher gravity beers so that I have more sparge water which increases efficiency.

One other big factor can be big beers and your mash tun capacity.