I'd imagine that in theory its for health screening / hydration levels, but the players knowing that they are going to be tested every morning, must focus their minds should any of them be out and about, and in a weak moment thinking about a few sneaky pints, etc!
One thing that is confusing me, from this, and various other youtube links posted over the last couple days. I presume its a mistake, but these seem to give the impression that is permitted for a player to SCORE direct from a free kick.