Should you ever add aromatic veggies to a dish without sauteing them first?
If the recipes were truly interesting in 'releasing the flavors', they'd be sweating the onions, not sauteing them.  Sauté is a higher-heat method that will cook the vegetables to create other chemical compounds, thus changing their flavor.

In the case of garlic and onions, this cooking makes them dramatically sweeter.  But sometimes you don't want that -- you may want the sharp bite of the garlic, and to do that, you need to add it near the end of cooking, without it having been cooked.

Also of note is that if you are cooking in an acid (such as tomatoes), the acid will slow or possibly stop the vegetables from softening ... so if you want your onions to dissolve into the sauce, they need to be cooked first.  If you them to add some chunkiness and the possible burst of onion when someone bites in, you want to add it later.

As others have noted -- in many cases, you'll add a given ingredient twice -- maybe some garlic to mellow out at the beginning of cooking, and then a crushed clove or two towards the end of the cooking.