[pavehawk2007]

A and T are "caller saved", meaning that if I want their value after I make a function call, I, the caller, must save the registers. So,

li t0, 10 call somefunc # Must consider t0 destroyed here unless we save it first

The saved registers are different li s0, 10 call somefunc # Can consider s0 = 10 here.

However, if we use the s registers, we have to make sure we put it back the way we found it. So, before li s0, 10, I need to save the old value of s0.