[reikonomusha]

This is correct. You can declare the types of objects (DECLARE TYPE) which has repercussions on size and allocation, you can declare the type of optimizations you want to do (DECLARE OPTIMIZE) be them speed space or safety, and you can declare things to be stack allocated (DECLARE DYNAMIC-EXTENT), avoiding GC of a particular object altogether.

[crispyalmond]

This is what makes CL feel so good to use. I can declare optimizations and types and verify it with DISASSEMBLE to see the resulting assembly. (If your CL implementation compiles to assembly, such as SBCL) It's possible to make things go really fast this way, too.