title: MIPS registers preservation
body: <p>So I'm learning MIPS right now and I saw on the MIPS green sheet that there are a total of 12 registers (including the s registers) that are preserved across a call. In my understanding of this, one must stack all such registers and retrieve them later when we want access to them again. </p>
  
  <p>However my question is if there was the trouble of going through this, why bother even using these registers? Is there a point of using these registers other than possibly running out of registers to use?</p>