Keep It Simple Silly! (or something like that)
We all know the acronym, but do we all apply it when it comes to mapping? Most of the time, the simplest solution is the most effective.
For example, I was given a map recently, where a child map was being called with a RUN() function, but it was ending with an error - "<Message>Disk write error</Message>".
Looking at the source for the child map, I could see that it was being used to rename a file. File in, file out, no fuss. The input and output Typetrees however, used a complicated repeating group structure, which was directly responsible (along with certain data structures) for the error reported. The Typetree being used was a copy of one from the parent. With data validation already done, there's no need to do it again.
Changing the Typetrees to simple text blobs on both input and output not only avoided this error, but probably gave the map execution a slight performance boost.
Map away, but keep it simple!