If you are refering specifically to the spells on this site; some do, some do not. Why is that? Because not everyone whom posts spells knows how legitimate magick works and rather instead, perpetuates fantasy garbage. Many legitimate practitioners post spells, forums, and articles however. But even then, if a spell works can depends on many factors! But for that I'm gonna go ahead and drop some wise words from Miss Weatherwax below along with some from Miss Lark.
Troubleshooting Spells by Weatherwax:
How To Write A Spell by Lark: