If you don't know what a jacketed fermenter is, it is a fermenter that has an extra "skin" on the outside of the tank that allows liquid to flow around the outside of the tank. By controlling the temperature of the liquid that flows around the outside of the tank, you control the temperature of your fermentation.
Commercial breweries do use jacketed fermenters for their primary fermentations. This is because fermentation is an "exothermic" process – that is, it generates heat. Because the tanks in a commercial brewery are quite large, the ratio of the surface area to the volume of the tank is low. As a result, there isn't a lot of surface area for heat to dissipate naturally. So, it is necessary to provide this extra level of temperature control to ensure that the product ferments at a consistent temperature, which is important for getting a consistent flavor profile.
For your home brewery, the ratio of the ratio of the surface area to the volume of the tank is much higher. There is a lot more surface area on the fermenter for every gallon of beer or wine. As a result, it is much less of a challenge to control the temperature of your fermentation – it is easier for the excess heat to leave the fermenter through the outside surfaces of the tank.
I have compared the temperature of my fermenting beer to the room temperature that the tank sits in, and it is almost always within 1 degree. Therefore, you can control the temperature of your beer by controlling the temperature of the room it is sitting in, or perhaps by putting it in a refrigerator with a good temperature controller on it.
The other thing to consider is that as a home brewer, you are not dependent on making a consistent product like a commercial brewery is. You will likely be happy if the beer is good, and if you are like me you seldom make the same recipe twice in a row, so the consistency from one batch to the next is not likely going to worry you a lot.
The cost of a jacketed tank would be too much for most people anyway, plus you have the cost of controlling the flow of the liquid that goes through the jacket (in a commercial brewery, they use a diluted food grade propylene glycol solution), which makes it all the more expensive.
The bottom line is that you don't need to have a jacketed fermenter for making quality home brew. There will be some people who are in it for the fun of building a commercial quality home brewery and they will no doubt enjoy the process of having a temperature controlled fermenter. For the rest of us that are more interested in just quality home brews, a regular conical does the trick just fine.
