This variable determines the maximum size of the stack cache.
Process stacks are cached and reused. When a process dies, its stack is put in the stack cache for future reuse if there are currently less than *default-stack-group-list-length*
stacks in the cache. Therefore if your application repeatedly creates and discards more than 10 processes you should consider increasing the value of this variable.
Note that stacks are allocated in generation 2, hence a program with a high turnover of processes may need to call (gc-generation t)
periodically unless all the stacks of dead processes are reused.
The default stack size is 64KB on all 32-bit LispWorks x86 platforms.
LispWorks User Guide and Reference Manual - 13 Feb 2015