I was playing with one the other day, causing the fluid to flow from one side to the other, which is divided by a piece of plastic that goes nearly to the top of the fluid tank. what is the purpose of this? my first guess is that it simply allows them to put less fuel in it, but that seemed silly upon further thought.
Probably to add rigidity and structural support. Multiple smaller cells are stronger than one large cell, and less likely to crack when crushed.
I always thought that it was to make the lighter usable when the fluid runs low. The amount of pressure forcing fluid up to the output valve is a function of fluid depth, so having the divider allows for lower fluid amounts to be at a higher height (and thus pressure) than they would without the divider. Of course, you do lose out on the volume the divider occupies…
I’m gonna vote for structural integrity.
I’m gonna vote for higher pressure.
So you can get the last bit up into the lighter. You run all the fluid to the side with the tube in it and can use it a lot longer.
I’m gonna vote for Great Taste.
Less filling?
lsmft
Uh, guys? Disposable lighters (like this) run on liquefied GAS. Butane, to be specific. While it’s liquid under pressure (to have more gas in small lighter), what actually burns is gas. That “empty” area above liquid is still filled with butane - in gaseous form. You don’t have to had liquid even touching feeding tube. Try it someday - mostly empty lighter work whether “fluid” is down, up, or sideways. Heck, it works even if you let all fluid flow into second compartment and hold it upside-down.
“Pressure” and “less fluid” explanations also don’t hold water - you could always make lighter smaller, or with thicker walls.
Q.E.D. is right - it’s for structural rigidity. And some lighters, mostly of unusual shape (round or ellipsoid) don’t have that divider.
thanks for the help, one less thing to ponder about keeping me awake 
Yes, but that is not how lighters work. It is not the liquid that passes through the lighter, but the gaseous form. Lighters will light when the wick is not immersed.
Side bar lighter trivia. I had a cheap lighter “pop” from sitting on a hot dashboard. I say “pop” versus “explode” because it didn’t ignite. I couldn’t figure out why my interior was covered in tiny pieces of plastic until I found the igniter. It was the cheap kind of lighter made of brittle plastic versus the more pliable type of plastic that would not shatter if struck.
Then why does the tube go to the bottom and for that matter why is there a tube at all 
It’s not a tube, it’s a kind of diffuser. It’s a porous material that’s designed to let the gas out, but not liquid fuel (which would be exciting, but dangerous).
Sorry QED, on re-reading the thread, I see you beat me to the correct answer.
Protip- If there is a small amount of fluid left, and the lighter won’t light, warm it in your hand for a minute. This will gasify the remaining liquid so the pressure will give you another chance at it.
Don’t smoke. Tobacco anyway.