It is, to the best of my knowledge, complete nonsense that on a newish macbook pro and air, that keeping it plugged into the wall damages the battery.
It was the case on older pc laptops, and most probably older macs too, but the newer macs are intelligent enough not to keep pumping power into the battery once it's charged.
Once the battery is fully charged, it's my understanding the computer stops putting power to the battery, and uses the power adaptor solely to power the computer.
I believe that this is what the green or red light on the magnetic charging connector signifies.
When it's green, the power is bypassing the battery, thus it's not damaging the battery.
When it's red, power is going into the battery.
Kind of the same as electronic cigarette battery chargers which flash red when charging, and green once they are charged.
You may remember in the news that some electronic cigarette batteries were exploding when they were left plugged in, before the manufacturers started using the different type of charger that cuts the charge, once the battery was at capacity.
My friend (who is the 'mac expert' in my circle of friends, and also a programmer) said that the way to check this is by waiting until your mac is 100% charged, then go to the top right of your screen and click on the battery icon, while the adaptor is still plugged in.
The menu that opens will say "battery is charged" and underneath it - "Power source: Power adaptor" which shows it's not using the battery to power the mac.
Then, unplug your charger and look at it and it will say "Power source: Battery"
Your battery cycles won't keep adding up if you keep it plugged in. And it won't ruin your battery, like older laptops.
The cycles will only start adding up when you use the mac without power, and then you recharge.
If you were to use the mac SOLELY with the power supply connected for the next week, you will notice your cycles will remain exactly where they are, because the battery isn't being used at all. It's just sitting there waiting to be used, should you unplug it.
I had the same concern when I first got my mac.
I was thinking that I had to unplug it when it was charged and was concerned I was gonna burn through my battery rapid style, as I work about 8 - 12 hours a day on it.
I was coming from a 2010 sony vaio where keeping it plugged in had damaged the battery. (It only stayed on for about 4 minutes unplugged!)
But, I was relieved to hear the MacBooks are smarter.
Check out what I am saying for yourself and try it out.
In short, I believe that keeping it plugged in does not damage the battery on a macbook pro & air(I have the 2014 pro retina 15" model) because the mac doesn't keep trying to charge a full battery and does not power the laptop at all with the battery when the power supply is connected.
Save your battery cycles to use during the times when you can't plug it in, to maximise the life of your battery.
The new systems are very clever and not like the older systems.
PS. here I have copy and pasted the info about my battery:
Charge Remaining (mAh): 8221
Fully Charged: Yes
Full Charge Capacity (mAh): 8221
Cycle Count: 20
Battery Installed: Yes
This shows that my battery is 100% charged, and still running at full capacity. (8221 mAh)
It also clearly states that the battery is not charging, and it's plugged in right now as I write this.
So I hope this gives everyone who is concerned about this some relief. And you can look forward to your battery lasting a lot longer than you initially feared.