You're on to something, with some exceptions.... *You mentioned the first, you'll get coarse flour. *Coarse flour = coarse baked goods. *You need fine flour for "fine" baked goods, such as cakes and pastry.
Second, you can't make very much at a time.
Third, you miss out on a lot of grains/beans/seeds by only using a coffee/spice mill, over a regular mill. *
As an example, I use a lot of bean flour in baking and cooking. *You can't do beans in a coffee/spice mill. *Bean flour is how I make "instant" refried beans. *NO soaking beans, NO long cooking. *Just add bean flour to water and boil for a few minutes.
- Softer grains mill better in a coffee/spice mill than hard grains. *If making gluten-free foods, a coffee mill is a fairly good way to save money by milling gluten-free flours that tend to be really expensive. *And as always - FRESH IS BEST. *Once the bran on any grain/seed is cracked, the oils in it begin to oxidize and go rancid. *The nutrients quickly degrade. *This is the #1 reason to mill your own flour - nutrition.
Some good uses for a coffee/spice mill.... *
Milling rice in a coffee grinder has always been considered a good way to "clean" it. *If you add that rice flour to a cookie recipe, you'll get really crispy cookies. *Use 10-20% rice flour in the recipe. *But rice flour will also cause the cookie to be gritty, so don't use too much.
Flour made from long-grain rice is good for breading, sauces, and used as a thickener, but NOT for baked goods. *Use medium- and short-grain rice for flour. *They will do the tasks mentioned for long-grain rice, but are also best used in baking.
For 1-cup rice flour, grind 3/4 c. minus 1 T. rice.
-FLAX - I mill flax in a coffee/spice mill (or my Porkert Seed Mill - great for grinding oily seeds - sesame, poppy, flax, etc., and tiny things like amaranth and teff). *Then I transfer it to a pint jar and keep it in the freezer. *I use 2 cups every 7-10 days. *I mill a pint (2-cups) at a time. *I add it to our morning kefir/fruit juice smoothie and all baked goods.
Use unroasted buckwheat groats for buckwheat flour. *You can get a "new" flavor by lightly toasting the buckwheat in a dry skillet - just until it releases its aroma. *Buckwheat mills cup-for-cup. *One cup groats makes 1 c. flour.
Freshly-milled millet turns rancid and bitter quickly, so only mill as much as you need. *Grind 3/4 c. millet to make 1 cup millet flour.
Barley adds moistness, similar to oat flour, to baked goods. * Barley is an "odd" flour. *It's light and airy after it's milled. *Flour made from 3/4 c. barley will initially measure 1-1/2 c. flour, but after several days in storage, it compresses to 1 cup. *Before measuring barley flour, tap the container on the counter a few seconds to settle the barley flour to get an accurate measure.
To make 1 c. barley flour, grind 3/4 c. lightly pearled barley (OR 3/4 c. minus 1 T. highly pearled barley OR 3/4 c. *PLUS 1 T. whole barley.
You can make your own oat flour by grinding oatmeal in a blender or food processor. *1-1/2 c. oatmeal (quick or old-fashioned) = 1 c. ground oat flour.