SCSIfreak is finally on the right track for the typical user (since very few of us try to cue multiple documents at the same time). Lets do the math:
Suppose you print something at 1200x1200 dpi on a standard 8.5"x11" paper with 1" margins all around. Each dot can be on or off (I will only discuss black and white laser printers here). Thus each dot is one bit or eight dots is a byte. Thus in each square inch you need 1200x1200/8 = 180,000 bytes. On that paper you have 6.5*9 = 58.5 square inches of data to print. Thus to cover the page you need 180,000 * 58.5 ~= 10 MB of memory. If you don't have a good compression scheme or an image that compresses easilly you will NOT be able to print it with just 2 MB of printer memory.
What happens instead? Most laser printers when they run out of memory will print part of the page on one piece of paper and a second part of the page on a second piece of paper (and 3rd, 4th, etc if you have that much data and are that low on memory). I've seen this happen in two methods. (1) Some printers print the top portion of the paper until it runs out of memory and the bottom section on the second piece of paper. (2) Some printers will divide up the data in a way that all data that is similar is printed on each piece of paper - such as text on one and the graphics on another. Either way you don't get your desired 1 page.
What can you do to work around it? Well the easiest thing is to bump up the compression (if your printer gives you that option). But that can significantly decay the quality of the print just like highly compressed MP3s or JPGs aren't as good as the original. The second thing you can do is drop down to 600x600 dpi. In most cases that won't harm image quality too much. But you are still left with 600*600*6.5*9/8 = 2.5 MB of data which might not fit your 2 MB printer memory. So then you must drop it down to 300x300 dpi - and then you will see significantly reduced quality on many prints.
I've seen this on dozens of printers. And my recomendation is 4 MB of memory minimum. If you print just text or simple graphics that are easilly compressed or have lots of white space then you might be fine with 2 MB. But try printing complex Word documents with multiple Excel graphs on the same page or complex graphics and you will quickly see the problems of just 2 MB.
Edit: My first laser was 1 MB and it was a worthless piece of crap that couldn't print a single Excel graph properly until I maxed it out at 4 MB.