The quicklisp/local-projects/ directory is just one
convenient place to put stuff, nothing dictates that you have
to put it there.
You can also put your own .asd systems elsewhere and set up
a call to:
(pushnew ".../my-projects/" ql:*local-project-directories*
:test #'string-equal)
(ql:register-local-projects)
Yes, you have to evaluate these two lines after making a
new .asd file. But if you put all your projects under
".../my-projects/" then nothing else has to change so it can
be part of a standard thingie you just call after setting up a
new experimental project.