Lithium battery chemistry is fiddly and kind of temperamental. The advice I've seen for Li-Ion and LiPo batteries is that discharging or charging the battery all the way damages it, and this damage is cumulative. I know that most manufacturers ship and store batteries at about a 40-50% charge, which is the point at which the chemistry is most stable. With LiPo batteries, a fully charged battery will lose some percentage of its storage ability for each month it's left completely charged.
COMPLETELY discharging most any kind of rechargeable battery is very harmful, and often can chemically damage or brick the cells. (this includes all but marine "deep discharge rated" trolling lead acid batteries) But this doesn't refer to discharging it to where the battery is "dead", this is
beyond that point. Modern battery packs don't allow you to dig that far down. Think of a battery's capacity as being able to go 5 to 10% into the red. The onboard controller in the battery won't let the computer drag it below zero. At that point it will say you are at 0% and will pull the plug. It's also saving some of that remaining charge to run the controller so it can "talk" with the computer and the magsafe (all three have a conversation when plugged in, before ANY power can be moved around) This conversation cannot occur if the battery is COMPLETELY dead, so it's important it never reach 'true bottom'. Otherwise it's bricked, regardless of the cells' condition.
If you discharge a battery to 0%, and then let it sit several weeks to months, it risks full self discharge and bricking by the above problem. When it gets to a certain point, (-5%?) it will start hibernating. This means you plug in the battery and power adapter and the computer outright doesn't
see any battery, because the controller isn't talking. It's hibernating. It will wake up briefly every 5 minutes or so to see if anyone is tapping it on the shoulder. If so, it then gets to talking, and the battery starts accepting a charge, recovering it from hibernation. This is why if you have a deeply discharged mac battery you just have to plug it in and wait. Although I've seen batteries take 5-10 minutes to start charging, I've also seen them take several
hours, so I'm speculating that at some point it shifts into "deep" hibernation, possibly only waking every 6-12 hrs, in a last-ditch attempt to save the battery. Several times I've left a computer with an undetectable battery on power throughout the afternoon with no appreciable effect, and then left for the evening, and come in the next morning to a fully charged battery. Those engineers are a clever bunch.
So discharging until it shuts off is still (afaik) Apple's periodic battery maintenance policy.
That being said, battery technology has made significant progress in terms of capacity, usable cycles, and memory. The somewhat recent shift from an expected 300 cycles to an expected 1000 cycles still amazes me. (people complain about non-replaceable batteries don't seem to understand, the battery is probably going to outlive the computer) Memory effects have been dropping steadily with time as well. Look at NiCD, and then NiMH, and LiIO, how that progression has gone. LiPO have very little problem with memory now. It wouldn't really surprise me if Apple stopped recommending periodic cycling, because a combination of increased mobile use and decreased sensitivity to memory are making it a rare/minor issue.
