not true...unless you have really light sand or a really powerful pump or if your tank is short leaving the intake close to the bottom.. i have sand in all my tanks and never suck any up.
it can and WILL ruin your impeller if the intake is left too far down. i had a penguin ruined that way on my 1st sand tank. kept getting stirred up and eventually ruined it within a few months. so be sure to leave the impeller atleast 1/2 way up the tank walls.
all my other tanks i leave the intake mid-upper levels in the tank, and have no issues what so ever yet in several years of using sand so far*knock on wood*
The trouble with any sand is in its diameter. The larger the diameter, the less likely it is to get stirred up beyond half way up your tank walls. You can, if you must, have very fine sand in your tank with powerheads, intakes etc as long as you either block the sands pathway with structure or apply a foam pre-filter to block the sands entrance to your pumps.