I read a really interesting article somewhere...maybe WPC, but probably somewhere else...about battery life and best charging practices.
So, as I recall, the gist was that a) modern batteries and USB smart chargers "take a break" when they reach 100%, as it is damaging to the battery to keep going, and in fact go idle until it drops down 2-3% and then start to top it up again. So if you find you're losing that top couple % quickly, it could be that you unplugged between top-ups.
b) that series of constant quick top-ups that happen when you leave a phone charging over-night is eating away at your battery's lifespan and holding power. The author claimed charging up before bed, unplugging for the night, and then plugging in for a quick 10 minute bump-up in the morning will get you the same result with less negative impact on the battery. Batteries are "rated" for a certain number of cycles...and it's usually a large enough number to be of little concern. But still, you're better off going at it with an icepick, rather than a sledgehammer. Part of that is letting the battery behave normally...regular recharging and discharging.
Beyond all that...I believe there's a certain psychological aspect to it.... It's the same as watching the gas gauge in my vehicle. I'm a lot more interested/invested in the top and bottom 20% than I am everything in between, which is just "the middle", and so am much more aware of changes near to, but away from, perfect/100%/full and increasingly towards screwed/0%/empty.
Having said that....not all batteries are created equal, and even from one manufacturing lot to another you can have variations.
I've noticed that Facebook and Flipboard require "hard closes" and will stay open if you just back out of them. I find those two will nibble away at your battery if left to their own devices.