Since you were looking for controversy, here's a little case for 2-line subs

Then I did something a bit more controversial. I made new copies and removed linebreaks in the subtitles where I deemed them unnecessary--when a single person talking stretches onto more than one line, for example. I retained linebreaks with things like song lyrics, where the subsequent lines were capitalized, but other than that a single person talking gets a single line. I did this for several reasons--first, the vobsubs were huge, so in some cases you'd have a mere 6 or 7 words split into 2 lines when they can easily fit on one if rendered at a reasonable size. I prefer for there to be fewer, longer lines because then the subtitles stay at the bottom of the image and creep into the frame less.
Two-line subs are used in a lot of DVDs and more intelligent fansubs for a reason -- it's simply easier to read short 2-line subs than long 1-line subs. Basically, it's not a matter of "vobsubs are too big to fit on 1 line"; the 2-line subs are intentional. As explained
here:first, our subtitles are often two lines (two short lines are easier to read than 1 long line because they can fit into your foveal vision and be read with little or no side to side scanning by your eyes),
Having 1 long line means that viewers have to spend more mental energy scanning across the screen reading the subs, thereby increasing the chance of missing out on other areas of the image. Same with having subs way down at the
very bottom of the screen -- viewers have to constantly "bounce" their vision downward to read the subs, and then back up to see what's going on. So in a way, 1-line subs at the very bottom of the screen spanning the entire width of the image (like typical fansubs) are
more "obtrusive" than short 2-line subs slightly higher up (like most DVD subs), because they demand
more active energy and attention to read. Also, subs that stay away from the very bottom and extreme sides of the screen won't get
hit by overscan on older displays, like if people are outputting to a CRT TV.
A given amount of text will always cover the same amount of space, regardless of how high it's placed or how many lines it's broken into. So if it's going to be covering screen space either way, it's better to make it easier to read. Besides, the human eye can interpolate what lies behind the letters. And if people absolutely must see something, they can always switch the subs off for a moment if the subs are soft.
That's why I intentionally put hard line breaks in the subs I work on. Fortunately, the same effect can be accomplished at the viewer level by increasing horizontal margins, which is what I do with most softsubbed fansubs and rips. Still, forced line breaks at logical points can make lines more coherent. For instance,
Go to the store and buy \N
a head of cabbage
is more coherent than
Go to the store and buy a
head of cabbage.
Now, I do agree with tweaking things to avoid 3-line subs, and I have seen some DVDs take it too far, like "How do \N you do?" in AnimEigo's Otaku no Video. Also, Aeigsub (the program most fansubbers use) has a spell-check, and you can also use Find+Replace to remove line breaks if you want to. Just search for \N and replace with a space or nothing.