Fan speed control

Nothing positive can come from using the hardware in ways unintended, especially something like a fan. If you have a heat dissipation problem because of the environment or misuse/abuse, then get yourself a cooling pad. And always elevate the rear of the computer at least 3/4 to 1" to improve airflow.

The computers are designed to run under certain temperature extremes. If you stay within those extremes there shouldn't be a problem. I'm pretty sure that Apple's engineers know more about heat dissipation than you do.

I don't see where lowering internal temperatures (within reason) could do harm. It could even prolong overall battery life. I know mine gets quite warm/hot and that definitely has to have an adverse affect on the battery. The life of other internal components such as HHD, optical drive, etc. would probably benefit from lower temps. The only negative that I can see is the fan life might be shortened.

Thanks for sharing more of your thoughts, but I think you missed my point as well. Put a discharged battery to charge in a MacBook Pro and the temps climb, as well as the fan speed, but the battery will still get hot. How hot depends on external factors and the fan speed. Increasing the fan speed will keep the battery cooler and prolong its life. What is the downside to better battery life?

Yes. Fan control is unnecessary. All MBPs (and non-Macs) run hot especially when playing games, watching videos, etc. This is perfectly normal. The computers SMC firmware will increase the fan speed as needed.

I think you missed my point. There are alternative ways to cool the machine if it's running too hot than increasing the fans idle speed. Fan control software just increases the fan's idle speed. The SMC increases the fan speeds as the temperature increases. So when your computer is sitting there doing nothing your fan is running at twice the normal idle speed. This doesn't help with anything except to keep the idle temperature lower at the expense of running the fans at higher speeds. If you don't understand the negative effects, then you need to rethink this out a little more.

All batteries get hot when they are charging regardless of the external environment. Blowing a fan on the battery doesn't prevent the heat generation.

Regardless, the real issue is whether the heat generated by the computer will shorten the computer's life. Over time the answer is, "Yes." However, when the computer is designed it is designed to function for an estimated period of time based on the temperature extremes for which it is designed. Unless the user is doing something that maintains operating temperatures at or near the upper extreme then the computer and all its components should last for the design life.

Now, my point was (and is) that Apple's engineers knew what they were doing when they designed the heat dissipation system in the computer. Since fan control software only ups the fans' idle speed, which does only a little additional cooling unless you run the idle speed over 4,000 RPM, there's really no need for the software. Fan control software does not increase the fans' maximum RPM (roughly 6,000.) The SMC still controls the fans' speed above the idle speed based on the information from the temperature thermocouples.

My additional point was that rather than tasking the fan for additional cooling that you use external means such as elevating the rear of the computer or using some sort of cooling fan. This accomplishes the same desired end (whatever that is) without tasking the fans.

Batteries are replaceable. Worrying over a few extra total hours of battery life seems a bit shortsighted.