I only use onion powder in things like "dry rubs", but I absolutely use garlic powder... As you taste things, you can slowly turn up the volume on the garlic by adding a few shakes of the Garlic powder... Sometimes things you used real garlic in can even use a boost... It also makes GREAT garlic bread... Toast a sliced baguette first to get it toasty, then spread butter, or a decent margarine (Brummel & Brown) with some garlic powder... Smear the toasty bread and put it under the broiler for a few seconds more... (People make the mistake of putting a garlic spread on untoasted bread and it never gets toasty...) I make a VERY popular chicken dinner in 5-10 minutes using Garlic powder... I pull all the meat off of a "quality" store bought rotisserie chicken and add it in chunks to a "bunch" of golden, fried (sautéed) onions... Then I add a can or two of Stewed Tomatoes, a "good amount" of garlic powder, a couple tablespoons of Balsamic, a good amount of grated parmesan cheese, a lil' sugar, and some dried Italian herbs... Cover and stew on low for a few minutes... You pour this decadent stew over a pile of mashed potatoes, rice, or polenta and you're livin' baby! ;c
In Italian cooking, garlic powder is considered vulgar. That being said, one of the best marinara sauce recipes I've tried uses garlic powder (a tiny bit) in addition to freshly chopped garlic.
I use garlic powder when I am out of the chopped garlic in the glass jar ;P I do use a lot of garlic powder when I am making an oil that I brush eggplant with: garlic, basil, Italian seasoning, kosher salt, fresh ground black pepper, and more basil I either grill this or bake it with grated Parmesean on top. YUMMY!
My wife and I go through many heads of fresh garlic each month, (sometimes many heads of fresh garlic in a week or weekend!) but that said, I still use a lot of garlic powder. Some things I demand fresh garlic, other things not - for some stuff I might prefer fresh garlic but I am too lazy and use garlic powder.