Lots of good stuff from other posters... I only have a little bit to
add.

It appears to be rather common for beginning and intermediate riders who
want more control to over-tighten boots and bindings. I think this is
usualy the result of boots that don't fit well enough. Simply put the
probability of finding the right pais of boots the 1st or 2nd time
around is pretty slim, unless you've been reading archives of this
newsgroup and then spent hours and hours shopping around ;-)
Tightening also gives the temporary feeling of more control, at least
until your feet start to ache or you need to make a quick corrective
turn.

As you get better you'll realize where the happy medium of tightness is,
and not go above and beyond that. (And eventually you'll get better at
selecting boots as well! It took me four tries to get it right!)

Back to the original topic - socks that don't slide aroun in your boots
might make it so you can loosen them a bit. I like medium thickness
wool socks, my current favorites are Wigman Sirocco , $9.00 USD, found
in discount sports stores. Every ski and snowboard shop wants to sell
me something super-thin that ends up being slippery. Something that
grips the inside of the boot works better for me.