THC in its "raw" form, as we know it, from cannabis plants, is in reality called THC-A (where the "A" stands for acid). By adding heat to the THC-A molecule, you "break" the connector between the acid and the product itself (THC). This is done to "activate" the THC in the bud before consumption. When smoked and vaped, you don't have to think about this. Since the heat from the flame and/or the heat from the vape coil will "activate" the THC when you inhale. Some deems decarbonation unnecessary when Cannabis is used in baking and general cooking, due to the heat of the oven or casserole/pan. But this has not been proven, so most people decarbonates their Cannabis when used in foods. Al of this becomes redundant if you're soaking your Cannabis is alcohol, since the alcohol breaks up the molecule and activates the THC upon contact.
You can still use Cannabis in cooking without activating it, and you'll still get a "buzz". But you'll get more out of the psychoactive compounds in THC by dissolvingit in alcohol or applying heat to it, making a more potent product.