Yes and no, depends on how hard you run your computer and how bulky the case is on your computer.
Your MacBook Pro is designed to dissipate heat through the aluminum by means of conduction teamed with the convection methods used with the fans and heat sinks located in channels throughout the body of the computer.
Without going deep into
Fourier's Law the general idea is that the fans pull air from intake located at the hinge (the black bar) on the back of the clamshell. If you look at the back of your computer you'll notice that the black bar is near flush when the computer is shut, and a small slit appears opening the passage for airflow when the lid is open. You'll also notice along the sides 3 small slits. These are the intakes for air flow which draw cool air in to draw the heat away from the components, similar to a strong gust of cool wind on a hot day. The heated air is then pushed out through the small slit in the back of the MacBook.
If it's run hard, the aluminum casing draws heat away from the components that it is connected to. Think of it as one big heat sink cooled by the room you are sitting in. It doesn't have as great of an effect as the fans inside, but it can lower the temperature a few degrees. In order for the process to work, the laptop needs to be sitting on a flat surface on it's rubber feet so air can pass under the computer. The airflow towards the vents help pull air under the device, it's the same thing as standing near a road and when a large truck passes you, you drift towards the direction the truck was going.
I wouldn't worry too much about cooling by conduction (aluminum body) as I would convection (fans) but make sure that your case does not block off the vents (including the one that snaps on the top).
In terms of case protection, dirt will get in between the hard case and the aluminum and it will leave dirty scratches in the aluminum. My suggestion would be to get a neoprene case for travel and leave it at that.
When it comes to cases in general:
Style
Protection
Cost
Now pick two.
[doublepost=1474901270][/doublepost]If you are interested in reading about laws, another good one is
Newton's law of cooling. And may more accurately describe how the aluminum dissipates the heat.