I do not need to rehash the benefits of relying on other libraries when developing a library here. If you care about dependencies, you ought to be familiar with those benefits already.
I wish to instead address the common complaint of "too many dependencies" from those who feel that getting a Common Lisp library installed is too difficult.
Here is how I feel about such requests:
In short, the effort avoiding a dependency, even in the case of synchronizing with an external source, far exceeds that for the simple process of fetching a dependency yourself and adding it to your ASDF registry. What's good for the maintainer is good for the library.
To clarify further:
a Mr. Fleming wishes to study bugs in smelly cheese; a Polish woman wishes to sift through tons of Central African ore to find minute quantities of a substance she says will glow in the dark; a Mr. Kepler wants to hear the songs the planets sing.