Though, be swift to recall: ability damage stacks,
while penalties from the same source usually don't stack. You can pretty much kill enemies from several attacks with a Wounding weapon, but you can't kill an enemy from two different uses of Ray of Enfeebling. Usually, as a rule of thumb, you can argue that penalties tend
not to stack; a Touch of Idiocy coupled with a Ray of Stupidity could be argued that don't stack (at least I know of DMs that won't allow them to stack), but RAW they would stack. Two consecutive Touches of Idiocy on the same target definitely won't stack. But, a cast of Bestow Curse to grant a Dex penalty and Shivering Touch
WILL most definitely stack and are excellent tactics.