Finally your software is complete! Ready to leave the nest of your development environment, spread its wings, fly into the wide world of unpredictable user environments... and crash. Deployment: the bane of software developers.
All of the subtle and not-so-subtle dependencies your application has on things in your development environment don’t necessarily carry over to the end users. Particularly the important parts: the packages, the runtime, the data files, and what-not.
Cue "wrapping", the method of choice for Tcl applications.