Hi,
No it won't hurt anything.
There are differing opinions on this. If you run on power adapter as much as possible, then you're saving "cycles" of which your battery has limited amount of. Age will also take its toll on a battery, no matter the usage. Some people will recommend running the battery down about 75% at once a month to keep it "exercised" which Lithium Ion batteries do need, but Apple has built that in to their charging circuit; after charging to 100% the battery won't charge anymore until it runs down to about 95% (which will occur naturally over time even with it plugged in), then charge it back up to 100%, etc. With multiple MBPs with Lithium Ion batteries, I have always let my Macs plugged in and let the charging circuit do its thing. I’ve never had to replace a battery. One of my batteries is going on 11 years running like that, although it has only a limited amount of run time now. I confidently continue that practice with all three of my MacBook Pros.
Apple says nothing about leaving your Mac notebook plugged in, so they don’t think it’s a problem either: http://www.apple.com/batteries/maximizing-performance/
