In the old days, custom flags had to be under 6KB. If you were right on the limit, you could try renaming your image to a single character, to save a previous few bytes.
Since then, the limit crept up to 10KB, then 12KB. Now we've raised it to 250KB. That's twenty times larger. Which would be more impressive if the old limit wasn't so insanely small. But still. It's never been easier to give your nation the swanky flag it deserves.
Bunch of technical details here.