刚开始看financial management，看得有点晕啊，有几个问题需要求教....
1.YTC和YTM的真正作用是什么？bond holder还是issuer更需要这些数据（特别是YTC这个指标）？
2. If, by the time the bonds become callable, the market interest rate had fallen below the YTM, and the bonds are called, the issuer can replace with new bonds paying lower interest.

If that happens in the above example, the original bondholders would earn the YTC of 7.137%, rather than the YTM of 8%
在这个情况下怎么得出我（Bond holder）更倾向于earn the YTC？