I'm a recovering RC maniac so I can answer this question in a bit more detail than you probably want.
Assuming you have a new laptop with a lithium ion or lithium polymer battery (do they even make nikel based batteries anymore?), the answer is do whatever you want. You won't hurt the battery. Just don't leave it uncharged for a long time. Here is why:
Lithium batteries have no memory effect (memory effect is based on a pattern of crystalization that affects total accessible capacity and is largely a phenomenon of nickel cadmium based cells).
When you charge a lithium battery, you are usually charging close to 1C (battery talk for 1 unit of capacity...4 amps for a 4 Amp hour battery...in practice it's usually less than this, but not by much). This is considered rapid charging. When you turn the laptop on, some of the charge current is diverted to run the lappy, lowering the current to the battery. The good news is, the battery doesn't care. It is just as happy (some say happier) charging at a lower current.
Believe it or not, lithium batteries are extremely volatile. If you charge them wrong, that is overcharge them, charge them at the wrong current, the wrong voltage, etc...they blow up. That is not an exaggeration...they literally explode killing everyone in a 50 mile radius (okay...that last part was a slight exaggeration...they only kill you, sometimes).
Lithium batteries have caused fires and killed people. About this, I am not joking.
This may sound alarming, but it's actually good news. It's good news because the charger in your laptop is a precision device, designed to charge your battery correctly under any condition you could think to subject your laptop too. And the battery itself has protective circuitry. The manufacturer goes out of its way to make sure of this, because they don't want you to sue them after your laptop kills your dog.
There is nothing (within reason) you could do to mess up your lithium battery. Nothing. Do whatever you want...feel no guilt.
Well...there is one thing. Lithium batteries do not like to be in a state of discharge. In fact, if a lithium cell drops bellow 3.0 volts per cell (typical lithium cells are 3.7 volts, so an 18.5 volt lithium battery is actually made up of five cells), it will never take a full charge again. And if you let it drop even lower, it will never hold any kind of worthwhile charge again. Ever. This is why when you find your old camcorder that you haven't seen in a year or two and want to watch that video of you and your ex girlfriend, you have to use the cord, because the battery won't hold a charge, even though it says it's full. I hate when that happens. But I digress...
The good news is, lithium batteries have a very low rate of self-discharge. Just don't store you battery uncharged for a long time (week if fully depleted, months if partially charged) and you will be fine. In a typical laptop, this is not a problem.
Also, a great improvement with lithium batteries is that unlike older NiMH and ancient NiCD (nickel based batteries) batteries, you can leave the laptop plugged in forever without any damage to the battery.
This is because of the cheapest and simplest way to charge nickel based batteries..."trickle" charging. The idea is that a battery can take indefinite overcharge if the charge current is very low. So the standard way to charge a nickel based laptop battery is to use a constant, never ending, low charge current...basically a "dumb" charger. The industry standard trickle charge rate is C/10, or one tenth of the battery's capacity (e.g. a charge current of 100mA for a 1 Amp hour battery). The theory is that you can leave a nickel battery charging at this capacity forever and the cell can take it. In reality, the batteries don't like to be trickled for a long time (especially the better NiMH cells) and battery damage occurs quickly when they are left to trickle forever. The only safe way to charge the older NiMH batteries is to charge them for no more than 16 hours at C/10, or to use a peak detection charger. None of which are too practical with laptops. Nickel batteries and laptops do not mix. That's why the older batteries lost so much of their capacity in a year or two.
Trickle charging is why it used to take all night to fully charge an older laptop battery. You will often hear people say "charge it over night". This is a relic of the old nickel days. Lithium batteries charge in a few hours, depending on the charge current the manufucturer decided on. Some laptops fully charge their battery in one hour.
I'll say it again to ease your mind after the whole exlposion thing....lithium batteries, because they are so dangerous if charged wrong, all come with regulating circuitry in the battery itself, as well as "smart" charging devices (I can't keep up with who is doing the thinking these days, the battery or the charger). The charge current and voltage are always regulated as the state of the battery changes. When the battery is fully charged, the charge current cuts off (remember that nifty little charge light that is only on when the battery is charging). So you can just leave the lappy plugged in forever, and the light will come on every once in a while when the battery voltage drops below full. Makes it easier to take care of your battery...because the battery essentially takes care of itself.
All of the old "charge it overnight", "don't use it until you charge it" and "don't leave it plugged in" wive's tales are just that...wive's tales. Not a single one fo them applies to lithium batteries in any way, shape or form.
A word of caution...lithium batteries, as great as they, are just batteries. They are "advanced" only because their dangerous nature forced people to make them that way, and their chemistry gives them a higher capacity/density ratio. All batteries, lithiums included, fade over time. There is no evidence to suggest completely draining lithium batteries hurts them, but that doesn't mean it might not be true. I would just use it however you need or want to and not worry about it. Remember, it exists to serve you, not the other way around.
I suppose I could have said all this simply by telling you "Do whatever the hell you want to your lithium battery except leave it uncharged for a long time". But that wouldn't have been any fun, plus I had to make sure you believed me.