My main machine these days is still my trusty four-year-old MacBook Pro. I've used it with the battery removed for a while to reduce heat and fan noise when in desktop use. Turns out to be a terrible idea.
It may not be a surprise to you but after spending hours last week trying to work out why my machine was so much slower than my colleages, I stumbled across the fact that MacBook Pros throttle their CPU to 1GHz when the battery is removed. This seems extraordinary. Turns out the 90W power supply isn't deemed enough to run at full speed so with the batty unavailable to provide burst power, you get crippled CPU performance.
I originally removed the battery as it appeared to aid cooling when my machine was in desktop mode. Now it is hard to tell if it actually was a thermal benefit or whether the cooler temperatures were only because of the crippled performance.
Either way here's a tip: don't work without a battery on an apple notebook unless severly reduced performance is enough for you.