There are few tools and appliances that are worthy of sitting on my counter full-time. My food processor is one of them and my coffee grinder is the other. But I don’t use the grinder for coffee. Of course you can use the grinder for coffee but mine is specifically designated for grinding whole spices.
I don’t think I would ever have the patience to use a mortar and pestle. The one time I tried, it nearly killed me. Way too much effort, it doesn’t work all that well and what a mess! A $20 grinder is a much better solution.
Quite often a recipe will call for toasted whole seeds which should be cooled then ground. That’s where the grinder comes in. Just place the amount you need in the grinder, recap the lid and whirl till it gets to the fineness you want. And that’s the other thing. You can control the coarseness or fineness of the spice. So many times I want cracked black pepper so I just pulse it one or two times and there it is. I do use my peppermill for small amounts of black pepper but anything over ½ teaspoon needs to come from the grinder.
I have used the grinder for whole peppercorns, cumin seeds, coriander, fennel (my favorite), anise and even cinnamon sticks. I’m sure it could tackle others as well. Many East Indian dishes recommend toasting those spices first, and then grinding. That is all possible in the coffee grinder (after they have cooled).
In my experience the coffee grinder grinds most evenly if it’s not overloaded (up to ¼ cup). Wipe it clean with a dry paper towel between changes and it that’s too much work just turn it upside down and gently tap it on the counter (that’s what I do).
If you enjoy barbequing I think it would be fun to create a signature spice blend for your meats using toasted seeds and passing them through the grinder. That seasoning mixed with a little oil and fresh garlic would be an awesome rub for grilled items.