Tires: Replaced 2 tires..., worn tires, rear tires

Question
I just recently (today) have had my two front tires replaced and they recommended I let them move the back tires to the front and put the new tires in the back. Is there a benefit to doing this? According to someone in my family, that's a WRONG WRONG BAD idea and I shouldn't have let them do that. I wasn't given any clear answer on the why's and how's so I was wondering if you could clarify that a bit for me because I'm getting extremely different advice here from two individuals. (the latter not having a whole lot of mechanical experience...)

Answer
Hana,

The reason you want to put the new tires on the rear is to prevent the rear tires from hydroplaning and causing the vehicle to spin.

New tires are less prone to hydroplaning and if the worn tires are on the front, then if the vehicle encounters  a lot of water and the front tires start to hydroplane, when the vehicle slows down, the front tires will grip, you'll still be pointed in the right direction and you can go on your merry way.  

But if the rear tires hydroplane first, it is very likely the vehicle will spin and when the vehicle slows down and the tires grip, you'll be facing the wrong direction.

There are some exceptions to the "Best tires on the rear" rule, like slow driving in heavy snow, but the rule works much more often then it doesn't.