There is still one case where Swapspace is less than helpful. When a process runs amok and tries to eat all memory it can as quickly as it can, Swapspace merely allows it to continue running until the process hits its address-space limits.
This is really a symptom of progress: memory-allocation sprees were once limited by physical memory, later by virtual memory, and now by disk space. Progress keeps removing the restrictive side effects of mechanisms, and sometimes we need to set policies to replace them.
For Swapspace the solution may be to disallow rapid successive allocation of swapfiles: "You can't have another swap file, you just had one!" The system can become quite unresponsive while allocating swap, so it's probably good to let things settle down a bit anyway.
That may be bad for situations where memory usage surges dramatically, but in those cases, the user may want other things to happen anyway: the surge may be a symptom of runaway processes, or of programs being greedier than the system can afford. If the surge happens infrequently, letting some programs fail may be acceptable. If it's not, the system needs either more memory or more permanent swap.
