I'm just taking the long view of the metagame. I don't see how anyone can justify slotting this into their deck over Abrupt Decay. I just can't.
- Abrupt Decay will deal with all of the enchantments that matter.
- -1/-1 sweepers just aren't strong enough; odds are that you'll only hit one guy, and Abrupt Decay would probably have done that for you (not many one-toughness creatures are 4cc or higher), plus be able to take care of creatures with higher toughness.
- That just leaves regenerating your side.
So the upside of Abrupt Decay is that it can't be countered and can destroy a hell of a lot more things than Golgari Charm can. The upside of Golgari Charm is that it can occasionally get you a 2-for-1 on creatures (assuming your creatures aren't dying too) and lets you protect your creatures from a single attack/boardwipe/kill spell (this is nuts if you can make it work in combat, otherwise it just reads "counter target spell that would kill one or more creatures you control").
The upside of Abrupt Decay is just so much higher that I would always run it first. And I can't ever imagine running 4 Abrupt Decays, and then thinking that I need Golgari Charm on top of that.
TL;DR: Golgari Charm isn't terrible. It's just horribly outclassed by another GB instant in the same set.
EDIT: Unless the metagame warps to where expensive enchantments matter. In which case I'd reconsider.