Do extracts add sweetness or just the flavor?

I really don't know how to best phrase this question, but do extracts add sweetness or just the flavor? That is, what should I expect from an extract?

For example, say I put maple extract into milk. Should I expect it to be the same as putting maple syrup in it if I use enough? Or if I put strawberry extract into it, is it then going to be as if I blended whatever amount of strawberries with milk without the added bulk of the fruit?

I guess I'm just a bit confused as to what I'm getting, since I've never used them before. I see a lot of baking recipes call for them, but then they also call for significant amounts of sugar on top of it, as well. What if you had, say, strawberry extract and just added more of instead of sugar. What would that do to the taste/sweetness?