Answer from cs61c-el (David Tung 16479725) for Question 1
This is a technique that works with leaf procedures, as it does not really apply with nested procedures.  The convention is that the 8 saved registers should be preserved on procedure calls (that is if they are used in  the procedure, they should be saved in the stack so that they can be restored to their original value when they exit the stack) while the 10 temporary registers do not have to be preserved (it is assumed that their data is not needed upon exiting, so their data does not need to be stored).