From this post, we can learn the reinvestment risk of coupon bond. It is worth noting that 1) YTM is attainable when roll rate is the same as YTM and 2) The argument that coupon rate is equal to YTM at issuance (par yield) is only applied to standard coupon bond with in arrears interest payment schedule. Unlike standard coupon bond, coupon bond with in advance interest payment has a higher YTM than coupon rate at an issuance.
Click through for the explanation as well as the R code used. H/T R-Bloggers.