http://fare.tunes.org/files/asdf3/asdf3-2014.html
Most CL implementations maintain their own heap with their own garbage collector, and then are able to dump an image of the heap on disk, that can be loaded back in a new process with all the state of the former process. To build an application, you thus start a small initial image, load plenty of code, dump an image, and there you are.
ECL, instead, is designed to be easily embeddable in a C program; it uses the popular C garbage collector by Hans Boehm & al., and relies on linking and initializer functions rather than on dumping.
To build an application with ECL (or its variant MKCL), you thus link all the libraries and object files together, and call the proper initialization functions in the correct order. Bundle operations are important to deliver software using ECL as a library to be embedded in some C program. Also, because of the overhead of dynamic linking, loading a single object file is preferable to a lot of smaller object files.