Because...
http://www.batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
"Similar to a mechanical device that wears out faster with heavy use, so also does the depth of discharge (DoD) determine the cycle count. The shorter the discharge (low DoD), the longer the battery will last. If at all possible, avoid full discharges and charge the battery more often between uses. Partial discharge on Li-ion is fine; there is no memory and the battery does not need periodic full discharge cycles to prolong life, other than to calibrate the fuel gauge on a smart battery once in a while."
http://arstechnica.com/gadgets/2011/02/ask-ars-what-is-the-best-way-to-use-an-li-ion-battery/
"One common misconception is that Li-ion batteries will only count charge cycles if the battery is drained completely in one session; another is that the battery counts one charge cycle for every instance the device is unplugged and plugged in again. Neither of these is true—Li-ion batteries actually count charge cycles based on a 100 percent discharge even when it's summed over multiple sessions. For example, if you discharge a battery to 50 percent one day, charge it back to 100 percent, then discharge it 50 percent again the next day, that is counted as one "cycle" of the battery. So shallow discharges, in all these regards, are ideal for a Li-ion battery."
http://www.chordelectronics.co.uk/chord-faq.asp#7
"Yes you can leave Hugo plugged into the charger. When the batteries are fully charged it will enter a low current trickle charging mode protecting the batteries from excessive charge. To prolong battery life, and enhance sound quality by isolating the Hugo from the external charging circuit, Hugo employs a sophisticated battery charge and maintenance system. If Hugo is left on without any charger connected, the batteries will be totally exhausted. Connecting the charger starts a battery recalibration cycle that might take several tens of minutes - then the LED will light and normal charging and operation will commence. This is quite normal and does not mean that the batteries are damaged”
BTW,
& and an electri(head)fying Happy New Year to all.