<p>I have this application installed on my Macbook Pro that allows me to disable a core on my CPU. It got me wondering: How does disabling a core affect the running processes?</p>

<p>I am also interested if disabling a core has an affect on the following</p>

<ul>
<li>Battery Life</li>
<li>Heat generation</li>
<li>Increased performance when the processor would normally be using less than 40% of both cores?</li>
</ul>

I don't know about power consumption, but I expect you would save some margin.  This depends upon the percentage of power used within the MBP by the CPU.
As for impact on raw processing power, it depends upon the nature of the applications you're running.  Most applications aren't designed to utilise multiple cores, although most top-end apps are.  So, if you're using Photoshop or video editing software then you'll notice a significant peak performance reduction in cases where the performance bottleneck is the CPU (and not network IO or disk IO).