Sounds like we need new(er) oven.
Baking cakes, cookies, etc--traditional. Convection for stuff that isn't as exact (like say, a potato casserole) b/c I don't feel like I "get" my convection oven's true power/heat level.
Me too Adam. I sometimes turn it on. It almost always guarantees I will overcook whatever I'm preparing. I'd love it if someone knew how to use the gd thing could share their knowledge..
When I was in college my parents got a convection oven that came with a guidebook of times and settings. Long story short, convection always (except when we'd put it on the setting that let it cook things itself).
My oven is not cool enough to convect, but traditionally you want to use it for (1) roasting things like whole birds, where having hot air move over the surface helps give you a nice crispy surface, and (2) baking things, where you want to avoid hot spots in the oven that will lead to uneven cooking. The basic physics are that hot air is made up of a bunch of particles that move more quickly when they are hot; they transfer heat to things they bounce off of. If you move the air, more particles bounce, so more heat is transferred. So anything in a convection oven will cook more quickly, which is why you want to turn the temperature down 25–50° when you use it, or dial your cooking time down by 25% or so and check your food often to make sure it hasn't overcooked.
Always. I don't see how it can ever hurt to spread the heat around more evenly, although it isn't a magic bullet, I still need to rotate and move cookies. In general though, I don't use the 25 deg reduction. I find that things just cook a tad faster, but without any noticeable change to the way they cook, so I shorten the time by 10% or so.
I can think of two cases when I'd hesitate to use one: (1) when the cooking process depends on steam, which the convection might disperse too readily (e.g., the no-knead-bread recipe that was popular a few years ago); and (2) when cooking something physically delicate, such as a soufflé. I could also imagine cases where you care about the relative rates of cooking the inside and outside of your item, but i'm not sure off the top of my head how that would play out in general.