Any risks/disadvantages of using MacBook Pro as a desktop? I have used iMac or Mac Pro for my Desktop system for the past 5 years but now consider replacing them with MacBook Pro Retina in desktop environment. The reason is mostly because I don't like bigger screens; 11 ~ 13inch for mobile and 15 ~ 21inch for desktop is the best combination for me. Also, I prefer the amalgamation of keyboard and trackpad as seen in the MacBook line.

However, I wonder there are any disadvantages of using MacBook Pro as desktop. Especially, because I have to open the laptop and run the system for the whole day/week/month, which is the way I have used Mac Pro or iMac, I'm worried how it influences the internal battery.

Is there any serious risk - e.g. increased chance of breakdown, or explosion or ignition for the worst - of letting MacBook Pro to run the system permanently, keep connecting it always to the AC adapter, and rarely shut down the system? Or does it just lead to the exhaustion of the battery life?

For your information I use 13' MacBook Pro Retina in mobile environment. I just want to use 15' MBP Retina as desktop and won't use it outside of home.

UPDATED

I want to handle my Mac much like President Obama does, which is the most comfortable posture for me...
You really hasn't stated you workflow but here is my thought:

The main disadvantage to me in this scenario is total cost by which I understand less powerful CPU/smaller screen for more money and also higher risk of getting into problems with GPU since it is the most failure prone component in notebooks as we see for years. And don't forget that a cup of coffee can cost as much as new Logic Board, Topcase and Labor.

For this scenario why don't you look at Mac Mini (preferably older 2012 Server QuadCore one with Intel HD4000) and as small monitor as you like? Or a smaller iMac with integrated Iris Pro and Quad i5? If you are so keen on Keyboard and trackpad being together look at Magic Wand and that trackpad is bigger than in Macbook.