"Do it once" approach is great... as long as it's not overdone.  I've inherited a system where all stored procedures and functions are written in this fashion. 

On one occasion I had to go though 6 nested SPs to get to the actual t-sql that performed business logic.  On other occasion I was trying to troubleshoot performance issues.  Again, the code used a function which was calling another function which in turn was calling another function etc.. When  looking at the execution plan I noticed that there were joins to same table multiple times from different functions.  I got rid of nesting functions and the performance improved 10 times.