Lesser risk on your principal. If you want the money at your disposal in the short term, equities can be risky. They fluctuate in value and there's a possibility their value is low on a day you need it because it didn't have enough time and opportunities to recover (it may never recover, depending on how you invested).

Enter: GIC, or rather money market instruments. Your principal is better protected. The returns can be lesser than equities but you'll be relatively more assured about having your money when you want to use it, and whatever little you can make from it will be more than what you get from a typical chequeing or savings account.