Substitution

I was signed up to bring the treats for our home group (bible study) last night. Since I only had one child yesterday (for a bit anyway), I made my way to the store and got what I needed to make a yummy fruit dip as well as some grapes and delish strawberries to go with it. I already had a box of brownie mix at home, so that's all I needed at the store. However, when I went to mix up the brownies I discovered that I did not have any vegetable oil.

Hmmm, whatever shall I do?? Typically when in silly cooking situations like this I call my mother. But she's out of town! I did the next best thing. I called my sister in law. My brother is always raving about what an awesome cook Carrie is, so it only makes sense to call her. So, call her I did.

Carrie suggested substituting the vegetable oil for olive oil. Hmm. Really? It won't taste weird? What does the oil do for the brownies anyway?

I didn't have many other options (none to be exact) so I used the olive oil, albeit a little less than what was called for (I was still apprehensive). The brownies turned out just fine and I couldn't detect anything strange about them, and people ate them. I ate them too, and seeing how I ate 'more than I should' I suppose that the olive oil passed the test.

So, here's my question: what does oil do in these recipes? Are there other things that could be used for substitution? Butter maybe? I know that applesauce could be used (Carrie told me that too, but I was fresh out) but again, what does that do in for the recipe?

I'm a cooking idiot, can you tell?

**Thank you Carrie for your advice!!!