The only reason you should attempt to manage fan speed is if you wish to control noise levels coming from your MBP. Otherwise, let OS X take care of it and don't worry about it
That makes no sense. All fan control apps only raise the minimum speed and never lower the max. You just cannot control noise levels, you can only raise them. All you can control is temps.
Just because Apple is a mulit billion dollar company means nothing. I am always surprised how gullible some people are. Apple has only interest in the components to last safely through the warranty period (3 years), after that it isn't so bad if a new hardware needs being bought.
Most chips are spec'd at operation temps to do just that which is last 3-5 years. Intel released slides once about that. Chips deteriorate and since laptop chips are often not 24/7 online but used much less they are trusted to survive real life 3-5 years on much higher temps.
In most cases other stuff fails before the CPU. Also 70C isn't yet all that bad. If you are like most people and not use a Notebook more than 5 years or not run it at high temps many hours a day it will probably you won't have to worry.
Some stuff lasts long and some isn't used all that much or hard so you can get much more than 5 years.
Still it is wrong to say Apple knows best. They have targets in mind. Thin form factor, as little noise as possible, last 3-5 years. "Best" is not as simple as that.
If one runs high load many hours a day it should go without saying that a desktop PC is better than a notebook.
