I own a Gene Cafe and was wondering why many across the internet recommend that the roaster is preheated before the roasting takes place, in comparison to the manufacture which claims that one should just add the beans and start the roasting straight away while everything is cold.
Preheating your Gene Cafe lets you choose between life cycle of the roaster and roasting consistency. By preheating your roaster, you should be able to get more consistent roast times. In my case my garage is sometimes 50F and sometimes 80F, so a preheat cycle would certainly probably help. I don't do it though. Any machine has a finite number of cycles, and you are shorting that window by preheating your machine.
I roast one and a half pounds a week (a half pound for work, and one pound for home). The half pound is always done by itself from a cold start. When I do the pound for home, I do two half pound batches, the first is from a cold start and the second is done immediately following on a "preheated" machine. I try to aim for the same roast level on each of the batches and the second one consistently needs less time to reach the same level. I generally set a timer and come back 14 minutes after the start. This allows me to fine tune the last portion of the batch, on cold batches I generally add a bit of time, and on the preheated ones I end up subtracting a bit (to get the same roast). I am fine with this as it saves me a cycle and will prolong the life of my roaster. However, I can see that some folks would want the roast length of two such batches to be much closer to the same at the cost of that extra cycle. For them it may make sense.
To keep the temperature consistent probably.
Some energy would be spent on preheating the roaster, and temperature will raise at the beginning from room temperature to roasting temperature. If you preheat the roaster it will be consistent all the time. I'm not sure it will affect the result much though.