Filling tart with beans/rice for baking I've found a recipe for a lemon tart: http://www.bbcgoodfood.com/recipes/380616/greggs-tangy-lemon-tart

Everything looks fine to me and I get what to do exactly, but I don't understand the part that says:


  Line the tart with foil and fill with rice or dried beans. Bake for 10 mins, then discard the foil, and bake for another 20 mins until biscuity.


I have got two closely related questions:


What is the purpose of this step? What would happen if I omitted it and baked straight for 30 minutes?
What type of foil should I use? I suppose it's not the plastic one since it would not survive the baking temperature of 160C. Or would it?
The rice/beans in this step act as a form of what are known as pie weights. They are used in order to maintain the shape of the crust as it is being baked. If you eliminate the weights during baking, you may encounter undesirable levels of puffing, curling and shrinking. If you'd rather brown the top of the bottom crust while baking, an alternative method often used is placing a second pie plate over the one containing the crust, and the metal should assist in browning the crust. 
Use standard foil.