For example, I’ve seen someone defining a package like so:
(defpackage :foobar
(:use :cl))
instead of:
(defpackage foobar
(:use cl))
Is there any actual difference? Or it’s just a personal preference, and has no effect on the program at all?
An interned symbol will hang around forever, adding load to GC, memory footprint, symbol clutter, etc. A non-interned symbol has nearly zero of any of these costs.
These are very minor considerations, perhaps only meaningful for release-quality library code.